Hi d,
Oh, that's a hard one. I think you are right to make some excuses instead of saying anything about being ill - I believe that people still have a lot of stigma about any form of psychological illness.
If I was in your position right now I think I would stick with my cover story with the boss, and share the truth here at PC or with your own therapist.
I am sorry that things are like this for you, I have been in a similar situation but my boss wasn't so sympathetic, so at least you have that on your side.
Good luck and good thoughts.
M