There are four stages of sleep:

• Stage 1: The first stage of sleep. It is a very light sleep. Stage one usually lasts just a few minutes. If the sleeper is not disturbed by anyone or thing, he or she will quickly journey into stage 2 sleep.
• Stage 2: This is a much deeper sleep than stage 1. Dreams start to brew around stage 2. Although there are no clear images, vague thoughts and ideas drift through the sleeper's mind. If the sleeper remains undisturbed, he or she will drift off into stage 3.
• Stage 3: A deeper sleep than stage 2. The sleeper's muscles are all relaxed by now, and his or her heart rate has slowed down. The sleeper's blood pressure is also falling. His or her breathing is steady and even. The sleeper is very difficult to wake now. Only two things can wake the sleeper now, a loud noise or an repetitious calling of the sleeper's name. Before long, the sleeper will venture into stage 4 sleep.
• Stage 4: The deepest sleep of all. This is the time the dreams occur. The sleeper is almost impossible to wake now. If there is a loud noise or if the sleeper is shaken, it will take the sleeper a few seconds to wake up. Both the sleeper's blood pressure and heart rate fluctuate, the sleeper's brain heats up. Then comes the REM (or better known as rapid eye movement). If the sleeper is woken up during this time, he or she will be able to remember a recently dreamt dream. The first REM period will last only about ten minutes. After that, the sleeper goes back into a deep stage 4 sleep. Again, the sleeper goes into a REM stage after a short period and cycles through REM and stage 4 until the sleeper is woken up.