The Mechanics Of Dreaming
Dreaming most frequently takes place during Rapid Eye Movement (REM) sleep, although it has also been noted to sometimes occur during stage 3 of Non-Rapid Eye Movement (NREM) sleep. It commonly takes place at least thirty to ninety minutes after one falls asleep. Before entering that phase, your mind will go through the preliminary sleep cycles of NREM sleep which correspond to three distinct stages of sleep.
When you start dreaming during REM sleep, several changes simultaneously occur. Your breathing can become erratic, and your blood pressure as well as heart rate will noticeably spike up. Your adrenaline levels will also shoot up, accounting for the sudden burst in brain activity. This sudden upward fluctuation in your brain activity and involuntary bodily functions contrasts with your body’s relatively low response rate during this period. While in a dreaming state, your body’s sensitivity to external stimuli decreases and your muscles are generally relaxed. Although one may note sudden movements and physical activity in people acting out their dreams while asleep, these people will generally not feel any pain when they accidentally hit objects while dreaming.
Although you may only be able to vaguely recall your last dream upon waking up, this does not mean that you only had one dream during the entire period that you were asleep. As a matter of fact, people usually have several dreams during one sleep period. A single REM phase can contain more than one dream, and a single sleeping episode may consist of several incidences of REM sleep. The four sleep cycles or sleep stages do not actually proceed in a strictly progressive manner. Instead, you may move back and forth from REM sleep to stage 3 of NREM sleep and then back again, and you may enter REM sleep at an average of four or five times during an eight-hour sleep period. If you’ve ever watched anyone while they were sleeping, you would have noticed that periods of dream activity are usually interspersed with periods of inactivity. The periods of activity correspond to active REM sleep while the intervals of inactivity correspond to the times when you revert back to NREM sleep.
Each dream phase or REM cycle may vary in length. It has been observed that the dream phases which occur at the latter end of one’s sleep period usually last longer than the earlier dream phases. This means that your brain will have longer dream phases the longer you are in your sleep. Differences in the lengths of the REM cycle have also been noted to exist among different age groups.