Consciousness describes a state where a person is aware of their surroundings and can respond to stimuli. Sleep is a normal state where a person is not conscious, but can still respond to certain stimuli, such as heavy touch, loud noises, or bright light. A person suffering a seizure also partially loses consciousness, although in some forms of seizure they may be aware of their surroundings. However, persons suffering a seizure are unable to respond to stimuli. Persons under general anesthesia are not conscious in order to prevent them from suffering pain. However, such persons can be brought back to consciousness by removing the application of the anesthetic.
As such, other forms of unconsciousness are always a sign of a serious medical condition. In such states, the patient cannot be brought back to consciousness without serious medical intervention. There are several causes of such unconsciousness, such as concussion, insulin shock, or blood loss.
There are five major classifications of loss of consciousness:
- Locked-in syndrome - The patient has awareness, normal sleep-wake cycles, and meaningful behavior
- Minimally conscious state - The patient has occasional awareness, waking moments, and meaningful behavior.
- Vegetative state - The patient has normal sleep-wake cycles, but no awareness or meaningful behavior.
- Coma - the patient lacks awareness and sleep-wake cycles, and has only reflexes
- Brain death - total lack of awareness, sleep-wake cycles, or behavior.