Sometimes, people just go
catatonic and freeze up. In such a case, hopefully, it's not a
hardware problem and there's no actual
brain damage. This
How To does not address such issues; look into
neurosurgery or something.
Other times, it's entirely a software problem. Yes, people can become so paralyzed by mental illness that they go comatose. Luckily, homo sapiens comes equipped with a reset button, though it really resembles the Mac's paperclip disk ejection system more than a button. Simply obtain the following items.
- A needle-less syringe
- A bucket
- Absolutely frigid ice cold water
The catatonic victim should be lying on a bed/cot/some flat surface. Fill the syringe with ice cold water. Put the bucket near their head. Now squirt the syringe-full of water into one of their ears.
If it's a mental illness problem, your coma victim will come to life vomiting profusely. Don't ask me why, it's something about the brainstem. Just one of those involuntary responses. Even someone with severe brain damage (but not brain death) will grimace or show some sign of discomfort, but someone whose coma is psychologically induced will probably go through the full response. While the patient will probably go back into the coma over time, now trained therapists can have a crack at helping the patient regain mental balance, and hopefully the cycle of coma->woken->therapy->return to coma will end in time.
Note: I am not a trained medical professional, though alex.tan appears to be one. For God's sake, don't try this at home. This knowledge should be used for good, not evil... though the temptation to try this out on my drunken roommate was almost overpowering sometimes, to be honest.