The most pronounced physiological changes in<unk>  occur in the brain. The brain uses significantly less energy during<unk>  than it does when awake, especially during non-REM<unk> . In areas with reduced activity, the brain restores its supply of adenosine triphosphate (ATP), the molecule used for short-term storage and transport of energy. In quiet waking, the brain is responsible for 20% of the body's energy use, thus this reduction has a noticeable effect on overall energy consumption.<unk>  increases the sensory threshold. In other words,<unk> ing persons perceive fewer stimuli, but can generally still respond to loud noises and other salient sensory events. During slow-wave<unk> , humans secrete bursts of growth hormone. All<unk> , even during the day, is associated with the secretion of prolactin. Key physiological methods for monitoring and measuring changes during<unk>  include electroencephalography (EEG) of brain waves, electrooculography (EOG) of eye movements, and electromyography (EMG) of skeletal muscle activity. Simultaneous collection of these measurements is called polysomnography, and can be performed in a specialized<unk>  laboratory.<unk>  researchers also use simplified electrocardiography (EKG) for cardiac activity and actigraphy for motor movements. Brain waves in<unk>  The electrical activity seen on an EEG is called brain waves. It has been revealed that the intensity of EEG waves on a frequency is related to one's<unk> -wake cycle. Meaning that the body is linked to certain waves at certain points during a person's day such as; being<unk> , falling<unk> , being awake. The model EEG waveforms seen are; Alpha waves, beta waves, theta waves, gamma waves, and delta waves are all seen in the different stages of<unk> . Each different wave maintains a different frequency and amplitude. Alpha waves are seen when a person is in a resting state, but is still fully conscious. Their eyes may be closed and all of their body is resting and relatively still, where the body is starting to slow down. Beta waves take over alpha waves when a person is at attention, as they might be completing a task or concentrating on something. Beta waves consist of the highest of frequencies and the lowest of amplitude, at this point a person is fully alert. Alpha and beta waves are the only waves seen when a person is in an awake state. Gamma waves are seen when a person is highly focused on a task or using all their concentration. Theta waves occur during the period of a person being awake, and they continue to transition into Stage 1 of<unk>  and in stage 2. Delta waves are seen in stages 3 and 4 of<unk>  when a person is in their deepest of<unk> . Non-REM and REM<unk> <unk>  is divided into two broad types: non-rapid eye movement (non-REM or NREM)<unk>  and rapid eye movement (REM)<unk> . Non-REM and REM<unk>  are so different that physiologists identify them as distinct behavioral states. Non-REM<unk>  occurs first and after a transitional period is called slow-wave<unk>  or deep<unk> . During this phase, body temperature and heart rate fall, and the brain uses less energy. REM<unk> , also known as paradoxical<unk> , represents a smaller portion of total<unk>  time. It is the main occasion for dreams (or nightmares), and is associated with desynchronized and fast brain waves, eye movements, loss of muscle tone, and suspension of homeostasis. The<unk>  cycle of alternate NREM and REM<unk>  takes an average of 90 minutes, occurring 4–6 times in a good night's<unk> . The American Academy of<unk>  Medicine (AASM) divides NREM into three stages: N1, N2, and N3, the last of which is also called delta<unk>  or slow-wave<unk> . The whole period normally proceeds in the order: N1 → N2 → N3 → N2 → REM. REM<unk>  occurs as a person returns to stage 2 or 1 from a deep<unk> . There is a greater amount of deep<unk>  (stage N3) earlier in the night, while the proportion of REM<unk>  increases in the two cycles just before natural awakening. Awakening "The Awakening", an illustration to writing by Leo Tolstoy Awakening can mean the end of<unk> , or simply a moment to survey the environment and readjust body position before falling back<unk> .<unk> ers typically awaken soon after the end of a REM phase or sometimes in the middle of REM. Internal circadian indicators, along with a successful reduction of homeostatic<unk>  need, typically bring about awakening and the end of the<unk>  cycle. Awakening involves heightened electrical activation in the brain, beginning with the thalamus and spreading throughout the cortex. During a night's<unk> , a small amount of time is usually spent in a waking state. As measured by electroencephalography, young females are awake for 0–1% of the larger<unk> ing period; young males are awake for 0–2%. In adults, wakefulness increases, especially in later cycles. One study found 3% awake time in the first ninety-minute<unk>  cycle, 8% in the second, 10% in the third, 12% in the fourth, and 13–14% in the fifth. Most of this awake time occurred shortly after REM<unk> . Today, many humans wake up with an alarm clock; however, people can also reliably wake themselves up at a specific time with no need for an alarm. Many<unk>  quite differently on workdays versus days off, a pattern which can lead to chronic circadian desynchronization. Many people regularly look at television and other screens before going to bed, a factor which may exacerbate disruption of the circadian cycle. Scientific studies on<unk>  have shown that<unk>  stage at awakening is an important factor in amplifying<unk>  inertia.
Sleep
Nightmare
Twilight sleep
Nightscout
Yawn
Conscious breathing
Window period
Morning care