Hello Polly, please let me welcome you to the forums.
What you have been going through and been subjected to, is illegal, it's discrimination because no one should be picked on if they have any mental illness, not by a mate at work or your boss and if your hours are cut down because of this then you are being bullied.
If your boss has done this with you, then surely you're not the only one, so if you report him, then hopefully other cases will appear, then your word would be more honest than what he says.
Polly go to your doctor and tell them, so it's then on record, if you need time off work then he will also help you, but don't feel as though your boss has won, he hasn't.
You sound to be a kind person and I don't want you to break because of your boss.
If you contact HR then your boss doesn't need to know an inquiry will take place, and don't forget about what other employees might have also mentioned in the past and if this has happened, that's even better for yourself.
Take some time off while you see a counsellor, there maybe others who have done the same.
Try not to worry, you are protected.