Why do we sleep? One way to study the need for sleep is to look at the effects of total sleep deprivation. It has been known for a long time that sleep has a detrimental effect; something used to good effect by the military for generations. The ancient Romans, for example, used tormentum vigilae (waking torture) to extract information from their enemies.
The effects of sleep deprivation over time are:
Night 1. Most people are capable of going without sleep for a night. The experience is tolerable if uncomfortable.
Night 2. The urge to sleep is much stronger, particularly between 3-5 a.m., when the body temperature is at its lowest.
Night 3. Tasks requiring sustained attention and mental calculations become seriously impaired. This is particularly the case if the task is repetitious and boring. Again, the early hours are the most crucial to needing sleep.
Night 4. From this night onwards, periods of micro-sleep occur. People stop what they are doing and stare into space for up to three seconds. The end of micro-sleep is accompanied by a return to full awareness. Confusion, irritability, misperception and the 'hat phenomenon' occur. In this, a tightening around the head is felt as though a hat too small for the head is being worn.
Night 5. On top of the effects previously mentioned, delusions (false beliefs) may be experienced. Intellectual and problem-solving abilities are largely unimpaired.
Night 6. Symptoms of depersonalization occur and a clear sense of identity is lost. This is called sleep deprivation psychosis.
Adapted from Huber-Weidman, 1976.
The effects of sleep deprivation are more psychological than physical. Reflexes are impaired but heart rate, respiration, blood pressure and body temperature show very little change. The main physical consequences seem to be hand tremors, droopy eyelids, problems in focusing the eyes and a heightened sensitivity to pain.
Interestingly, we seem able to catch up with sleep in a much shorter time than was lost through deprivation. A person who loses three nights of sleep might only need a slighted extended sleep in order to feel fully refreshed.