The problem of chronic insomnia is serious enough that there are over 100 sleep-disorders centers throughout the United States and many other programs that study the nature of sleep. Each one is characterized by very different brain wave patterns with most of the activity occurring in the right hemisphere of the brain. In the early stages Alpha waves predominate, then sleep spindles appear in the brain as wave patterns slow down. Next, brain waves slow down even more and the spindles disappear. Then Delta waves appear and you are deeply asleep.
Delta waves are high in amplitude and slow in frequency.
In this stage you may be difficult to awaken. You are also more prone to sleeptalk, sleepwalk, and have nightmares. Everyone dreams during this stage whether the dreams are remembered or not. The dreams of this stage are somewhat disorganized and don't make sense like those in the next stage do. This is the last stage of sleep before the cycle repeats itself.