As the 90-minute mark is approached, there is a reversal of this pattern and stage 4 yields to stage 3 and then back to stage 2 followed by a transition to dreaming or REM sleep. These are the loss of sleep spindles, k-complexes and slow waves with a pattern close to stage 1 in the EEG, the complete loss of skeletal muscle tone and episodic bursts of conjugate and rapid eye movements. The first dream episode is rather brief and may last only about 10 minutes. It is followed by another cycle of sleep like the first and transitions into another REM sleep episode, which will be a little longer. These would represent quotas for a healthy young adult.
Sleep usually terminates at the end of the last dream episode.
There is a spontaneous transition to wakefulness associated with the feeling that you are through sleeping. Your body temperature, heart rate and blood pressure have been steadily declining toward their daily nadir while you slept. There will be a small but definite rise in heart rate and blood pressure when you stand up and a rise in body temperature. Your baseline heart rate, blood pressure and body temperature will each steadily rise to their peak values by late afternoon along with most mental and motor function skills. It is these inherent changes associated with other physiological processes that support wakefulness.