A coma is when a person is in such a deep state of unconsciousness that the individual is unable to be awakened. Severe illness and injuries such as concussions and brain trauma are the most frequent causes of comas. It derives from the Greek word koma, meaning 'deep sleep."
A coma is also called a persistent vegetative state. That means that a person who is comatose is not able to respond to the environment; in fact, he or she is not even aware of the surroundings, even though the person could appear normal. Although their eyes may open in response to stimuli and parts of the body could make spontaneous movements, the person does not talk or react to commands.