Sleep state refers to the appearance of a person during sleep. There are four stages of sleep relative to waking state, sleep, light sleep, deep sleep, and continue to sleep, each cycle can be divided into four stages of sleep.
The characteristics of each stage are as follows:
Phase I (or phase I): Sleep phase Start with drowsiness, fall asleep, and stop waking up. At this time, the breathing slows down, the muscle tone drops, the body is mildly relaxed, and at this time it is the initial state of sleep, sleepers are more likely to be aroused by external sounds or triggers.
Shallow sleep stages
Phase ii (or phase ii): Light sleep stages, or light sleep stages.
This stage sleep is shallow sleep or mild to moderate sleep, the sleeper is not easily awakened, at this time the muscle is further relaxed, the eeg shows the fusiform sleep wave.
Deep sleep stages
Phase iii (or phase iii): Deep sleep, when the sleeper enters deep sleep, the muscle tension disappears, the muscles relax and the sensory function is reduced further and less likely to be aroused.
Continue deep sleep
Phase iv: This stage is an extension of the third stage, but not every sleeper can reach this stage, and not every sleep cycle can reach.
Some people don't get enough sleep to get to this stage, or only the third and fourth stages of sleep.