The state of consciousness is generally classified according to the degree of arousal and the content of consciousness. Patients are classified according to the degree of arousal of consciousness, which is divided into wakefulness, drowsiness, lethargy and coma, and coma is further divided into three different degrees of coma: light coma, medium coma and deep coma. If classified by altered content of consciousness, they are mainly divided into blurred consciousness and delirium. Both types have decreased awareness and responsiveness to the surrounding environment, disorientation is also impaired, and patients with delirium even have impulsive and aggressive behaviors. There are also special types of disorders of consciousness, including decortication syndrome, deafferentation, agnogenic mutism and vegetative state. Many patients with these disorders of consciousness appear to be awake because they can open and close their eyes on their own, and they can even rotate their eyeballs to follow an object, which makes them appear to be awake, but they have no communication with the outside world, and their consciousness has been lost.