The stages of sleep. While we sleep, we go through a series of stages which differ in their brain-wave patterns and physiological conditions. At this point, stage one begins. This stage lasts for only a few minutes of light sleep. We experience a lowering of body temperature and blood pressure, relaxation of our muscles, and a slowing of our breathing and heart rate.
Brain waves are slow and low-voltage.
We are now in a deeper sleep, and more difficult to awaken. Our muscles relax. During stage three, we become more relaxed, and we experience a decrease in heart rate, body temperature, blood pressure, and respiratory rate. We spend about 20 minutes on this level, which is characterized by profound muscle relaxation, difficulty in awakening, and a majority of our brain waves within delta. When we leave stage four, we ascend through stage three and two and one.