"Sleep is not tangible" or what the Hebrew tradition has to say about sleep.

Much of what is known about sleep disorders has been uncovered in the last forty years. As scientists, we consider these discoveries to be landmarks. Yet there is a tremendous amount of information written about sleep in the Bible and its commentaries. Sleep, and even sleep disorders, are referred to in many instances and can be directly interpreted by what we know today. Our forefathers and foremothers generally viewed sleep as both pleasant and necessary and were aware that sleep was not one continuous stage. They referred to the function of sleep as being restorative. They deplored sleep deprivation, believing that it impaired life. They felt that excessive sleepiness was harmful. They understood that insomnia could be caused by stress and anxiety and by excessive alcohol, and that physical activity (exercise) and drinking milk could improve sleep. They suggested cures for insomnia, including some of the ideas included in today's sleep hygiene rules. They understood that there was a rhythm or timing to sleep. They even understood that it is easier to delay the circadian rhythm that to advance it. Although naps are not recommended, they sometimes took naps in the afternoon, but suggested just how long that nap should last-about one-half hour. And they knew that with age, although sleep is advanced, healthy elderly do not have difficulty sleeping. Although we think we have discovered many new features about sleep disorders, much of what we know today was suggested thousands of years ago and documented in the Bible and the Talmud.