When you are dreaming, you will notice that your body has many changes that happen. You will have an increased blood pressure and your adrenaline will rise. Your heart will beat faster, and you will have hyperactivity, and this is why some people die when they are sleeping. Sometimes the heart is not able to deal with the harsh changes that the body has during sleep.
When you go into REM sleep, or Rapid Eye Movement, it is a time where your eyes will move back and forth very fast. This happens in the fourth sleep stage and it accounts for around 20% of the time that you are asleep.
When you fall asleep, it takes around 90 minutes for you to reach this stage and you will be able to go through the four stages of sleep from 4 to 7 times each night.
When you are in REM sleep, you will have an increased heart rate and blood pressure. Your body will go through a lot of things, but your muscles and your body cannot move and will stay completely relaxed. Even if you move a lot when you are sleeping, during REM sleep you do not move, and this is sometimes even called “REM Paralysis” because you are not able to move.
With REM sleep, your mind is active just as if you are awake but the chemicals in your body are different. Your cholinergic neurons and your noradrenaline and serotonin chemicals change. The serotonin becomes missing while you are dreaming, and the chemicals allow the brain to do the tasks such as remembering things and solving problems. This is why it is hard to remember your dreams sometimes.