I cut myself in my back yesterday (yes, in my back. I was aiming to hurt myself in a way that it'd hurt with every movement I make) not thinking of the fact that I have physical therapy tomorrow morning and will have to take off my T-shirt.

What should I do? Should I warn him before he sees it? I have half a mind to say "I should tell you - I hurt myself Saturday and I have some cuts on my back as a result" (He knows I am depressed and have been suicidal (including suicide attempts) in the past, while he was treating me) before taking off my shirt. Or would it be better to just take off my shirt and wait for him to say something, then say "I cut myself"? Or should I just say nothing at all/say "I don't want to talk about it" or something?