See also: Sleep as an altered state of consciousness.
Sleep is needed for survival, and disallowing oneself to sleep for an extended period of time could be fatal, but foregoing it can also result in less significant (physical and psychological) side effects. There are three types of sleep deprivation:
Total sleep deprivation is associated with severe consequences such as disorientation, delusions, and significant mood changes, whereas partial sleep deprivation is associated with more minor effects such as lack of motivation, poor motor coordination and some memory problems.
REM sleep and NREM sleep do not have exclusive functions – they are both responsible for physical and psychological needs – however, it is commonly accepted that a loss of NREM sleep will result in more physical effects, whereas a loss of REM sleep will result in more psychological effects.
NREM sleep deprivation may result in:
REM sleep deprivation may result in:
Interestingly, sleep deprivation does not often impact completion of complex or challenging tasks, but makes simple tasks a lot more difficult.
The effects of sleep deprivation are, mainly, temporary. Only in very extreme cases (such as total sleep deprivation for a very long time), may consequences linger. In some very severe cases, total sleep deprivation may lead to heightened vulnerability to disease, or death.
Sleep deprivation can usually be recovered without making up for the total amount of sleep we have lost; following deprivation, we may sleep slightly longer, but eight hours of sleep lost, for example, does not equate to eight hours added to the next time we sleep. How much sleep is required to make up for sleep deprivation is likely to depend on numerous factors, including age, what type(s) of sleep has been missed, and genetic makeup.
REM rebound occurs, unsurprisingly, following a deprivation of REM sleep. It involves a significantly higher proportion of REM sleep (compared to NREM sleep) during the night, during which dream intensity increases.
When we are very tired or sleep-deprived, we may experience a microsleep. A microsleep is a very short (3-15 seconds), involuntary period in which we sleep during wakeful behaviour. The individual usually does not notice that they have fallen asleep during this time, and continues their behaviour as if nothing has happened.
There are two kinds of cycles: ultradian rhythmed and circadian rhythmed.
Whilst the above tends to be consistent for all people, we are likely to experience different sleep-wake cycles during our lives:
During infanthood, an individual is likely to sleep around sixteen hours per day, which aids in growth and development. This will steadily decline toward adolescence.
During adolescence, we are likely to experience a delayed onset of sleep and need for sleep. That is, the sleep/wake cycle will shift toward the evening, whereby we are more likely to both go to sleep and wake up later. The reason for this is biological: melatonin (a hormone which induces sleepiness) and cortisol (a hormone which induces alertness) are both delayed in release, meaning that it often takes longer to ‘wind down’ at the end of a day, and longer to wake up in the morning.
This ‘night owl’ sleep/wake cycle tends to return to a regular adult sleep/wake cycle by the age of twenty-one (sometimes slightly earlier for females).
As suggested above, an adult’s sleep/wake cycle tends to be earlier than that of an adolescent’s. Teenagers may require slightly more sleep than usual, but adulthood tends to come with sleep stability. That is, adults generally require 7-9 hours of sleep per day.
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