When the night is quiet and we are about to go to sleep, our bodies often twitch suddenly. This kind of twitch is often referred to by scientists as lethargic nystagmus (also known as sleep twitch). At present there is no research to fully understand its cause, so There is a lot of speculation about this. One explanation is that the human brain evolved based on the reptile's brain, so it still retains part of the reptile's stress response pattern. When the muscles are completely relaxed, the brain will be based on this stress The reaction mode thinks that we are falling freely. For the sake of self-protection, the brain commands the muscles of the whole body to move immediately, trying to catch something during the fall, so the already relaxed muscles will suddenly tighten, causing sleep twitching. This text? ['Introduce the clinical manifestations of sleep nystagmus.', 'Provide an explanation for lethargy.', 'Explain the relationship between sleep nystagmus and the brain.', 'Explain the significance of lethargy muscles for humans.']