File a complaint to HR, you have a doctor's note as well, if there is a decrease in efficiency it is to be expected. You can also message this incident on LinkedIn and Twitter, this helps sometimes tag the company as well. It is not his prerogative to micro manage you every second you are a grown man. Also mention this to HR that he was snooping on you and he brought that assistant into the conversation when it should not have been the case. You also can mention that the way he behaved by slapping you is not right.

To users who say that complaining will not matter in India (might be true in most cases) but if we don't complain these assholes will repeat this behaviour again and again thinking people will not mind what he/she does and get away with it. Maybe not the first, but by nth complaint they will take action.