system
Given the following post, respond as if you're commenting on Reddit:
human
At what point does someone stop sleeping and start being in a coma?

Do they get pronounced to be in a coma after one day? Two? Or is it the circumstances under which they fall asleep?
gpt
A person is considered to be *comatose* if they, for a period lasting **longer than six hours**, cannot be awakened, don't respond to external stimuli, lack a normal sleep-wake cycle and do not act voluntarily.

(source: Weyhenmyeye, James A.; Eve A. Gallman (2007). Rapid Review Neuroscience 1st Ed. Mosby Elsevier. pp. 177–9. ISBN 0-323-02261-8.)