Every person I've ever talked to with diagnosed mental illness has always worried about it being fake at multiple points. I'm no better; when I'm in the middle of some of my worst mood swings, i.e. I'm tearing things off my walls and dissociating, I'll message my friend and tell her I'm making it up. It's normal to wonder if you're making it up, but if it's causing you distress and it keeps happening, it's probably real.