The term 'state of deep unconsciousness' can be summarized by the four-letter word 'COMA'. A COMA is a state of prolonged unconsciousness in which a person cannot be awakened and does not respond to pain, light, or sound. It is caused by damage to the brain, such as from a stroke, traumatic head injury, or drug overdose. Comas can last for days, weeks, or even months, and can result in permanent disability or death.