The amount of sleep each person needs depends on many factors, including our age. Infants generally require about 16 hours a day, while teenagers need about 9 hours on average. For most adults, 8 hours a night appears to be the best amount of sleep, although some people may need as few as 5 hours or as many as 10 hours of sleep each day. Women in the first three months of pregnancy often need several more hours of sleep than usual. The amount of sleep a person needs also increases if he or she has been exercising strenuously, learning new skills or has been deprived or sleep in previous days. Getting too little sleep creates a "sleep debt", which is much like being overdrawn at a bank. Eventually, your body will demand that the debt be repaid. We don't seem to adapt to getting less sleep than we need. While we may get used to a sleep-depriving schedule, our judgement, reaction time and other functions are still impaired.
People tend to sleep more lightly and for shorter time spans as they get older, although they generally need about the same amount of sleep as they needed in early adulthood. About half of all people over 65 have frequent sleeping problems, such as insomnia, and the deep sleep stages in many elderly people often become very short or stop completely. This change may be a normal part of ageing, or it may result from medical problems that are common in elderly people or from the medications and other treatments that the elderly use for these problems.
If you feel drowsy during the day, you may not have had enough sleep. Microsleeps, or very brief episodes of sleep in an otherwise awake person, are another mark of sleep deprivation. In many cases, people are not aware that they are experiencing microsleeps. The widespread practice of "burning the candle at both ends" in countries such as Australia and America has created so much sleep deprivation that what is really abnormal sleepiness is now almost the norm.
Many studies have shown sleep deprivation is dangerous. Sleep deprived people who were tested by using a driving simulator or by performing a hand-eye coordination task perform as badly as, or worse than those who were under the influence of alcohol. Sleep deprivation also magnifies alcohol's effect on the body, so a fatigued person who drinks will become much more impaired than someone who was well rested. Many people try to offset the effects of sleep deprivation by using stimulants such as caffeine. However, caffeine and other stimulants cannot overcome the effects of severe sleep deprivation. The only real solution is to modify the lifestyle to include an adequate level of sleep, or seek professional help if the sleep deprivation is due to insomnia or some other health condition.