REM Sleep (Rapid Eye Movement)
During REM Sleep, breathing becomes rapid and irregular. Eyes are very active at this point as this is a dream state. Commonly, REM sleep happens about 5 times a night depending on the person. Heart rate and blood pressure also typically raises.
The picture below shows the length the brain waves at each stage of sleep.
What exactly Are These Brain Waves?
So what exactly are these brain waves that are spoken of? The brain emits millions of neurons that send signals all at once. This cause of course causes tremendous amounts of electrical activity that can be read from using medical equipment such as an EEG ( which can measure electricity levels that come from the brain).
The diagram above shows different lengths of each kind of brain wave.
Beta: Consciously alert -|- Alpha: Mental relaxation but still semi-alert -|- Theta: Reduced consciousness -|- Delta: Very deep sleep