Sleep is actually a very complicated process. Sleep has several components, and the ratio of time spent in these different types of sleep is very important. If the ratio of time in the various stages of sleep is changed, the sleep is not as restful as it should be. Some diseases, some drugs, and outside influences may disturb this complicated and delicate balance.

Fortunately, if the body is given the chance to get enough undisturbed sleep, it will automatically adjust the ratios of the different kinds of sleep, and eventually resume a normal balance.

In the sleeping state, the brain is very active. In fact at times, it is more active than when awake. The brain has characteristic wave forms when sleeping.

There are two kinds of sleep: Rem sleep, which involves vivid dreaming, and non-rem sleep. In people, non-rem sleep accounts for about 75% of the sleep time. The brain is less active during non-rem sleep.

Other animals spend much greater amounts of time in rem sleep. Some researchers say that kittens spend almost all their sleeping time in rem-sleep. Kittens will almost always be twitching while sleeping, and this shows they are in rem sleep.

Researchers do not know why REM sleep exists. During REM sleep the brain is very active. It is creating a complete world, that the sleeping person then interacts with this dream world. During this period you are protected by a sleep paralysis. This system projects a signal down the spinal cord that turns off the neurons, and it is likely this is partly responsible for the intense reality of the dream world.