Brain waves during sleep are mainly theta and delta waves, which are related to the depth of sleep. When we are about to fall asleep, the human body is in a deeply relaxed, stress-free subconscious state, and at this time the brain waves are mainly theta waves. After falling asleep for a period of time, the human brain can be in a deep sleep, unconscious state, at this time the brain waves are mainly δ waves. Besides, when the human body is learning and thinking, the best brain wave state is alpha wave, which is one of the basic states of the brain. In times of tension, stress and brain fatigue, the brain wave state will be β wave. The human body has its corresponding brain waves in different states of consciousness, thus promoting the brain to do its job better. Sleep is a level of consciousness, and the energy of brain waves can be measured by professional instruments, which can be used to distinguish sleep from other consciousnesses and to observe the quality of sleep.