Circadian rythm is regulated by the suprachiasmatic nucleus in the brain and is set onto an internal clock lasting a day, and triggers sleep through the release of melatonin. There are two systems triggering sleep: the circadian rythm, and the sleep pressure. Stress or lack of food can reduce the capacity to sleep. Certain birds can sleep half of their brains. Sleep patterns in animals can be different. The natural pattern in dicyclic: 8h at night, and 1/2 to 1h mid afternoon. Humans require about 8h of sleep per night. Primordial function is still uncertain, however it evolutionary cost (given the vulnerability during) tells it must be important Sleep is common to all animals including insects, so its evolutionary origin is ancient. Half life of caffeine is up to 10h so it’s sometimes hard to trace back sleeplessness to coffee intake Sleep hygiene requires a consistent sleep schedule, a cool and dark room, avoiding liquor and caffeine and slowing down before going to bed. Why we sleep is not certain, but sleep seems to bear several functions, both of the biologic (drain adenosine and such) and psychologic (what Walker calls: overnight therapy). Ideally a 30m to 1h nap in the early afternoon.

Sleeping less, even 6h, is associated with issues on every aspects of life: medical, cognitive, emotional. 7 to 8h (more 8) of sleep are necessary every night (that is - sleep opportunity). Sleeping is a need second only to eating and drinking. “ Unlocking the Power of Sleep and Dreams ”

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