General terms:
* Unconsciousness: This is the most general term for being unaware of your surroundings.
* Stupor: A state of near-unconsciousness, characterized by sluggishness and decreased responsiveness.
* Deep sleep: This can be used metaphorically to describe a state of deep unconsciousness, but it's not a medical term.
More specific terms:
* Vegetative state: This refers to a state of wakefulness without awareness.
* Minimally conscious state: This is a state of partial consciousness, where there is some evidence of awareness.
* Brain death: This is a legal and medical term for the irreversible loss of all brain function.
Informal terms:
* Out cold: This is a colloquial term for being unconscious.
* Knocked out: This is another informal term for being unconscious, usually due to an injury or anesthesia.
It's important to note that the most appropriate synonym will depend on the specific context and the level of formality required.