The state of consciousness is generally classified according to the degree of awakening and the content of consciousness. Patients are classified according to their degree of consciousness awakening into wakefulness, drowsiness, lethargy and coma, and coma is further classified into three different degrees of coma: superficial coma, moderate coma and deep coma. If classified by the altered content of consciousness, it is mainly divided into blurred consciousness and delirium. Both types have decreased awareness and responsiveness to the surrounding environment and disorientation, and patients with delirium even have impulsive and aggressive behavior. There are also specific types of disorders of consciousness, including decortical syndrome, decerebrate, inactive 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 their eyes can even follow objects and appear to be awake, but they have no communication with the outside world and have lost consciousness.