Many things. I don't think we know exactly what can make unconsciousness last so long, but there is a huge variety of things that can make a person so sick that their brain chooses to shut off for any amount of time.

Different things can cause a coma, like ramming your head to hard against something, brain injuries or a few illnesses. Sometimes doctors put you in a coma, because you would die otherwise.

A comma is a punctuation mark indicating a pause in the train of thought briefer than that marked by a period.

A coma is a medical condition in which someone is unconscious and typically cannot be woken for longer than is natural for human sleep cycles.

A coma is what happens to your body. A comma is a punctuation mark.

A comma is a pause in a sentence. A coma is a pause in your life.

What's the difference between coma and comma?