Are you suggesting that you should put your friend in a coma? Otherwise the things from the real world that they couldn't see or hear would still be affected by their actions while they are in their own little world.
There is one rational answer: Get them to see a doctor, they have depression. The doctor will very likely put them on medication that will have all the effects you want without making them go totally insane. With luck, treatment will run it's course and your friend will get back to full mental health. And, whatever you do, don't leave them in the hands of an amateur hypnotist who thinks (s)he can do what you're suggesting.