When we think about the history of sleep science, the story is often told as a leap from ancient Greek philosophy to modern medicine. But a new study shows that medieval physicians made several profound and interesting discoveries when it came to how we sleep.
A review article by sleep specialist Ahmed S. BaHammam argues that medieval Arabic and Persian physicians developed a “sophisticated understanding of sleep and dreams.” Drawing on figures such as al-Rāzī (Rhazes), Ibn Sīnā (Avicenna), Ibn al-Nafīs, and others, his paper shows that medieval scholars were describing, classifying, and treating sleep-related problems in ways that often sound strikingly familiar today. Here are ten of the most remarkable “discoveries” and insights highlighted in the study.
Schematic Timeline of Key Developments in Sleep Science from Medieval Arab-Islamic Scholars (8th–13th Centuries CE).
1. Sleep was a sign of recovery from illness
One of the simplest but most important observations comes from al-Rāzī: that if a patient was sleeping normally, it was a sign that they were improving after an illness. Modern medicine similarly notes that sleep supports immune responses and accelerates healing processes.
2. Testing treatments with comparison groups
Al-Rāzī is also credited with something that looks surprisingly like early clinical comparison. In one passage, he describes treating one group of meningitis patients while deliberately withholding bloodletting in another group to observe differences in outcomes. Severe insomnia appears among the warning signs he tracks. While this is not a modern clinical trial, it shows a clear attempt to use structured observation and comparison in medical reasoning.
3. A clear medical description of sleep paralysis
Centuries before sleep paralysis became a common subject in modern medicine, al-Rāzī gave a vivid description of the condition he called al-kābūs (the nightmare): “When the nightmare occurs, the person feels something heavy pressing upon them and finds themselves unable to cry out.” This account aligns closely with modern descriptions of sleep paralysis, which was first noted by a European physician in the 17th century.
4. Two different types of sleep paralysis, two different treatments
Even more striking, al-Rāzī did not treat sleep paralysis as a single, uniform problem. He divided it into a “gastric” type and a “brain-centred” type, with different underlying causes and different preventive strategies. For the gastric type, he focused especially on diet and avoiding heavy evening meals—an early example of tailoring treatment to an underlying cause.
5. Bedwetting explained through deep sleep
The paper also notes al-Rāzī’s discussion of nocturnal enuresis (bedwetting). He linked it to deep or prolonged sleep and to relaxation or weakness of the bladder and sphincter muscles, and he offered practical advice such as limiting evening fluids and avoiding excessively deep or prolonged sleep. Here, a sleep-related physiological state is clearly connected to a specific clinical problem.
Primary source manuscripts from key medieval Arab-Islamic medical texts. (A) Manuscript folio from Al-Rāzī’s “Kitāb al-Ḥāwī fī al-Ṭibb” (The Comprehensive Book), demonstrating the Arabic medical textual tradition and scholarly documentation methods used in medieval Islamic medicine. (B) Illuminated opening page of Ibn Sīnā’s “al-Qānūn fī al-Ṭibb” (Canon of Medicine), showcasing the sophisticated artistic and scholarly presentation of medieval Islamic medical manuscripts. Both manuscripts exemplify the rich intellectual tradition of Arab-Islamic medical scholarship that established foundational contributions to sleep science and general medicine. Source: Wellcome Collection. Licensed under Creative Commons Attribution 4.0 International License (CC BY 4.0).
6. A medieval version of “sleep hygiene”
Long before the modern phrase existed, al-Rāzī laid out a set of recommendations that look very much like sleep hygiene advice. He writes:
Those with disturbed sleep and frequent insomnia should avoid hot and spicy foods and consume moisture-balancing foods like lettuce and squash, bathe in lukewarm water before sleep, take light walks, and avoid troubling thoughts at bedtime. If these measures prove insufficient, sleep-inducing medications such as poppy syrup or violet oil applied to the temples may be used.
The emphasis is on routine, environment, and habits before medication.
7. A theory of how sleep begins and ends
Ibn Sīnā (c. 980–1037) expanded the discussion by trying to explain what sleep actually is. In his Canon of Medicine, he defined sleep as “the return of the psychic spirit from the instruments of sensation and movement to the source, whereby these instruments cease their actions due to this withdrawal, except for those necessary for survival, such as respiratory instruments.” While we would not accept this model today, it represents a serious attempt to explain the sleep–wake cycle.
8. A medieval description of obstructive sleep apnoea
Ibn Sīnā believed it was best to begin sleep while lying on the right side and later switch to the left. He also makes one eye-catching claim that looks like a very early clinical description of obstructive sleep apnoea: “those who sleep on their backs experience tongue relaxation backward, blocking the respiratory passage and causing snoring and choking.”
9. Sleep as an active, brain-initiated process
Ibn al-Quff (d. 1286) offered an innovative account of how sleep begins, modifying Ibn Sīnā’s framework by arguing that nature actively induces sleep. He proposed that preventing the dissolution of internal fluids relaxes the nerves and blocks the entry of spirit into the sensory and motor pathways, so sleep results from an active, brain-initiated redirection of the spirit rather than passive depletion. He also linked this mechanism to sleep’s restorative purpose, claiming that the redirection helps optimise physiological repair and mental rest.
10. The idea that the brain is not simply “off” during sleep
Finally, Ibn al-Nafīs (1213–1288) challenged the notion that sleep is a total shutdown of the brain. He argued that while external senses and voluntary movement rest, internal faculties such as imagination remain active during sleep. This provides a framework for understanding dreams and reinforces the broader point that sleep is an active physiological state, not mere inactivity.
BaHammam also points to other advances made by medieval physicians, including the use of various medicines to assist sleep and the interpretation of dreams. He concludes:
Many observations and recommendations made by medieval Arab-Islamic civilization physicians have been validated by contemporary sleep research. Their recognition of sleep’s immune function, understanding of the importance of circadian rhythm, appreciation of dietary influences on sleep quality, and emphasis on sleep environment optimization align with current evidence-based sleep medicine practices.
Ahmed S. BaHammam’s article, “How golden age Arab-Islamic scholars revolutionized sleep physiology and dream analysis,” is published in Journal of Taibah University Medical Sciences. Click here to read it.
Ahmed S. BaHammam is a Professor of Pulmonary and Sleep Medicine at King Saud University, Riyadh.
Top Image: Bibliothèque nationale de France MS Latin 9333 fol. 97r
When we think about the history of sleep science, the story is often told as a leap from ancient Greek philosophy to modern medicine. But a new study shows that medieval physicians made several profound and interesting discoveries when it came to how we sleep.
A review article by sleep specialist Ahmed S. BaHammam argues that medieval Arabic and Persian physicians developed a “sophisticated understanding of sleep and dreams.” Drawing on figures such as al-Rāzī (Rhazes), Ibn Sīnā (Avicenna), Ibn al-Nafīs, and others, his paper shows that medieval scholars were describing, classifying, and treating sleep-related problems in ways that often sound strikingly familiar today. Here are ten of the most remarkable “discoveries” and insights highlighted in the study.
1. Sleep was a sign of recovery from illness
One of the simplest but most important observations comes from al-Rāzī: that if a patient was sleeping normally, it was a sign that they were improving after an illness. Modern medicine similarly notes that sleep supports immune responses and accelerates healing processes.
2. Testing treatments with comparison groups
Al-Rāzī is also credited with something that looks surprisingly like early clinical comparison. In one passage, he describes treating one group of meningitis patients while deliberately withholding bloodletting in another group to observe differences in outcomes. Severe insomnia appears among the warning signs he tracks. While this is not a modern clinical trial, it shows a clear attempt to use structured observation and comparison in medical reasoning.
3. A clear medical description of sleep paralysis
Centuries before sleep paralysis became a common subject in modern medicine, al-Rāzī gave a vivid description of the condition he called al-kābūs (the nightmare): “When the nightmare occurs, the person feels something heavy pressing upon them and finds themselves unable to cry out.” This account aligns closely with modern descriptions of sleep paralysis, which was first noted by a European physician in the 17th century.
4. Two different types of sleep paralysis, two different treatments
Even more striking, al-Rāzī did not treat sleep paralysis as a single, uniform problem. He divided it into a “gastric” type and a “brain-centred” type, with different underlying causes and different preventive strategies. For the gastric type, he focused especially on diet and avoiding heavy evening meals—an early example of tailoring treatment to an underlying cause.
5. Bedwetting explained through deep sleep
The paper also notes al-Rāzī’s discussion of nocturnal enuresis (bedwetting). He linked it to deep or prolonged sleep and to relaxation or weakness of the bladder and sphincter muscles, and he offered practical advice such as limiting evening fluids and avoiding excessively deep or prolonged sleep. Here, a sleep-related physiological state is clearly connected to a specific clinical problem.
6. A medieval version of “sleep hygiene”
Long before the modern phrase existed, al-Rāzī laid out a set of recommendations that look very much like sleep hygiene advice. He writes:
Those with disturbed sleep and frequent insomnia should avoid hot and spicy foods and consume moisture-balancing foods like lettuce and squash, bathe in lukewarm water before sleep, take light walks, and avoid troubling thoughts at bedtime. If these measures prove insufficient, sleep-inducing medications such as poppy syrup or violet oil applied to the temples may be used.
The emphasis is on routine, environment, and habits before medication.
7. A theory of how sleep begins and ends
Ibn Sīnā (c. 980–1037) expanded the discussion by trying to explain what sleep actually is. In his Canon of Medicine, he defined sleep as “the return of the psychic spirit from the instruments of sensation and movement to the source, whereby these instruments cease their actions due to this withdrawal, except for those necessary for survival, such as respiratory instruments.” While we would not accept this model today, it represents a serious attempt to explain the sleep–wake cycle.
8. A medieval description of obstructive sleep apnoea
Ibn Sīnā believed it was best to begin sleep while lying on the right side and later switch to the left. He also makes one eye-catching claim that looks like a very early clinical description of obstructive sleep apnoea: “those who sleep on their backs experience tongue relaxation backward, blocking the respiratory passage and causing snoring and choking.”
9. Sleep as an active, brain-initiated process
Ibn al-Quff (d. 1286) offered an innovative account of how sleep begins, modifying Ibn Sīnā’s framework by arguing that nature actively induces sleep. He proposed that preventing the dissolution of internal fluids relaxes the nerves and blocks the entry of spirit into the sensory and motor pathways, so sleep results from an active, brain-initiated redirection of the spirit rather than passive depletion. He also linked this mechanism to sleep’s restorative purpose, claiming that the redirection helps optimise physiological repair and mental rest.
10. The idea that the brain is not simply “off” during sleep
Finally, Ibn al-Nafīs (1213–1288) challenged the notion that sleep is a total shutdown of the brain. He argued that while external senses and voluntary movement rest, internal faculties such as imagination remain active during sleep. This provides a framework for understanding dreams and reinforces the broader point that sleep is an active physiological state, not mere inactivity.
BaHammam also points to other advances made by medieval physicians, including the use of various medicines to assist sleep and the interpretation of dreams. He concludes:
Many observations and recommendations made by medieval Arab-Islamic civilization physicians have been validated by contemporary sleep research. Their recognition of sleep’s immune function, understanding of the importance of circadian rhythm, appreciation of dietary influences on sleep quality, and emphasis on sleep environment optimization align with current evidence-based sleep medicine practices.
Ahmed S. BaHammam’s article, “How golden age Arab-Islamic scholars revolutionized sleep physiology and dream analysis,” is published in Journal of Taibah University Medical Sciences. Click here to read it.
Ahmed S. BaHammam is a Professor of Pulmonary and Sleep Medicine at King Saud University, Riyadh.
Top Image: Bibliothèque nationale de France MS Latin 9333 fol. 97r
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