The average person spends roughly one-third of his whole life sleeping. Sleep is vitally important to our health in that it regenerates the body and rejuvenates the mind. Sleep is comparable to a recharging period in which we switch off normal consciousness while the body goes through the vital process of restoring itself and stocking up energy for the next day.
While we aren't normally conscious during sleep, this doesn't mean that our brain is inactive. During sleep, our body goes through a predictable, repetitive axle consisting of various stages, namely:
Stage 1 - Transition period from wakefulness to sleep;
Stage 2 - Light sleep;
Stage 3 - Deep sleep;
Stage 4 - REM sleep.
The cycle is repeated throughout the night, from Stage i through 4 and then back again. Typically, a person goes through four up to seven repetitions of this cycle in one night.
In the fourth stage, or the rapid-eye-movement (REM) stage, there is noticeably increased brain activity. This brain activity is in fact greater than that in normal waking moments. The REM stage of sleep is when dreaming occurs, which indicates that while we dream, our brain becomes highly active. At this exact same time, the muscles of the body become completely paralyzed. This is presumably a built-in safety mechanism to prevent our bodies from physically acting out our dreams or whatever it is that our mind is thinking. Some dream researchers hypothesize that during REM, the brain busily processes the day's experiences and events, and probably other related events that happened in the more distant past. It could also be "rehearsing" for future events, playing out possible scenarios that could happen based on past experiences, more recent events, the person's fears and hopes, and many other associated factors. Dreams are then the by-product of all this mental activity.
Though this theory makes sense, there is of course no way of confirming it. It is nearly impossible to know what the mind really "thinks" or occupies itself with while we are asleep and unconscious.
So far, what has been established scientifically are these dream facts:
For most adults, REM sleep takes about 15 to 10% of the total sleeping time. The first REM stage is usually experienced 30 to 90 minutes from the time a person falls asleep, and this is when dreaming can begin.