REM sleep is recognized by tiny twitches of facial muscles and slight movements of the hands. Blood pressure rises, breathing and heartbeat become faster, eyes dart rapidly around the eyelids under closed eyelids as if looking at a moving object and, if you are a man, you may have an erection. Researchers have discovered that when sleepers are awakened during REM sleep they typically say they have been dreaming. (You may also feel temporarily paralyzed if awakened during this stage, as if something malevolent is pressing down on you; this phenomenon can explain the supposed succubus, incubus and alien abduction experiences.)
Most of the dreams you remember occur during the REM stage when the brain is fully active. After about ten minutes of REM you enter stages two, three and four again, and keep moving backwards and forwards through the sleep cycle. As the cycle continues, however, the REM phase gets longer and longer with the longest phase being around thirty to forty-five minutes. Of all your dreams during all the stages of REM and NREM (it has recently been discovered that we can dream then too), the final REM stages are the ones you are most likely to remember.
Because sleeping and dreaming are so crucial, your brain may sometimes demand the sleep it needs so that you don’t get into mental or physical overload. That’s why you may sometimes drop off for no apparent reason when you’re traveling by car or train, or watching TV.
Research on sleep-deprived animals shows that sleep is necessary for survival. For example, whilst rats normally live for two to three years, those deprived of REM sleep survive only about five weeks on average, and rats deprived of all sleep stages live only about three weeks. Other studies have shown that subjects repeatedly awoken during REM—which means they were deprived of dreams— become anxious, bad tempered and irritable. This suggests that sleep is vital for physical rest and repair, and REM sleep, when we are most likely to dream, is essential for our emotional well-being. Therefore, although we still aren’t sure about the whys, whats and hows of sleep and dreams, it’s possible to conclude that the reason we sleep is to dream.Dreampedia | Dreampedia