While the topic is focused on sleep, allow me to share with you the five different stages of sleep. It may take your interest to observe a person who sleeps and pinpoint which stage of sleep he may be in.
The first stage is Alpha. This is the stage that the muscles relax. Blood pressure, body temperature and heart rate begin to decrease. This is the time that the body is in its meditative state or relaxed level.
The second is True level of sleep. In this stage, brain and body slows down further.
Third is Deep level of sleep, wherein the body functions slows further down.
Fourth is Deepest sleep. This more or less begins 30 to 60 minutes from Alpha stage. Senses are turned off. This is the stage that your body undergoes restoration and rejuvenation. This is when your body starts to replace what was spent during your waking hours. A very interesting stage, to say the least.
The REM (Rapid Eye Movement) is the last stage. It is when all your muscles are suddenly paralyzed for one purpose. That is to prevent your body to react to your dreams. This lasts around 50 to 60 minutes and has been proven to be beneficial to sound mental and physical health.