What happens to our body as we dream?

We dream during our REM sleep, our body scarcely moves as most of our muscles are quasi paralyzed during that time, only the muscles needed for breathing and eye movement are really active. Our brain is extremely active and our eyes move rapidly from one side to the other even though our lids are closed; our blood pressure increases, as do our breathing speed and heart rate, causing our body temperature to rise like if we were awake and our genitals to be erect (unless circulatory problems exist). The most active part of our nervous system is the one that creates the emergency response (also known as fight-or-flight response), which is the sympathetic nervous system.

This type of sleep has a restorative effect in our mind, it organizes the information we got through our senses, most of it when awake, and removes information that is not relevant. It is now known that REM sleep is a key element for learning and memory. That is the reason why it is soooo important to sleep enough before a test, and why people that stay up all night studying for the test retain so little of what they studies, compared to students who actually had some sleep, specifically a whole cycle of REM sleep (at least).

How often do we get REM sleep in a good night’s sleep?

We enter REM sleep every ninety minutes approximately, which accounts for about three to five times per night considering that the first time we enter REM sleep is only for a few minutes but its time increases progressively over the course of the night to about thirty minutes. If we add our sleep time in REM, we learn that it is about 25% of our sleeping time.
In a good night’s sleep we alternate between sleep types (REM and non-REM sleep); most of our deep sleep happens during the first part of the night, as most of our REM sleep happens towards the morning. It is important to note that sleep patterns do change as we age.