sleep was restricted to 5 or 6 hours per night (6), (7), (8) for several nights. Notably, participants who are allowed to sleep for only 6 hours per night for 12 nights responded as slowly as other participants did after one night without any sleep at all (8). Additional changes associated with similar total sleep loss include decreased short-term memory, poor performance on newly learned or complex tasks, and difficulty maintaining attention (9). In addition, individuals report increased sleepiness and decreased positive mood after sleep restricted to five hours per night (10). It is of further concern that, although the time required to fall asleep decreases and the quality of performance deteriorates as the number of nights of sleep restriction increases, an individual's perception or subjective assessment of his or her sleepiness starts to level off after a few days. Thus, individuals may develop some tolerance to feelings of sleepiness over a few days, and this may make it more likely that sleep restricted people will be unaware of their continuing deterioration in alertness and performance (8). This can have profound personal and public safety consequences (e.g. safe motor vehicle operation, ability to make critical work and family decisions, etc.).
The studies suggest that the degree to which sleep duration is commonly restricted in the community may compromise alertness and performance. However, because it becomes a chronic condition, sleep loss may be unrecognized by the sufferers who accept it as their norm. Some clues to an overly sleep restricted life include need for stimulants like coffee to wake up or get going each morning, difficulty remaining focused and productive when sitting for a while, negative mood, or poor memory.
Sleep Extension or Prolonged Sleep Duration
While it is clear that short sleep duration engenders a variety of adverse health and social consequences, few studies have examined whether longer than usual sleep times improve performance or alertness. One investigation sought to encourage college students to "sleep as much as possible" over several weeks (11). The study participants increased their total daily sleep time from 7.5 hours to 9 - 9.9 hours