i love you. i’m lucky.
It’s not uncommon for people who have previously experienced obsessive compulsive symptoms, but not to the degree necessary to meet diagnostic criteria for OCD, to be pushed over the diagnostic threshold by a traumatic event. PTSD and OCD have a relatively high co-morbidity, and post-traumatic OCD is itself a thing.
Tony’s work on the suits is pretty clearly a compulsion (mark 42, anyone?)—it temporarily relieves his anxiety, but he has to keep doing it. No number of suits is enough.
Honestly, the end of the movie does not say to me “And now he’s fine!” (Although Tony may certainly think that.) For one thing, his compulsions were ultimately validated—that is, if he hadn’t built all those suits, he and/or Pepper might well be dead.
And even if they hadn’t been, that doesn’t mean he won’t react similarly to stress in the future. But that’s okay, too, and the story resonates more closely with my own experience that way anyway—you get worse, you get better, bad shit might happen again, you might very well get worse again, hopefully you get better again, too. You probably don’t get “cured,” but you can learn to live with it.