Yeah, if you don't buy into the whole "Tony Stark is a super genius" then things don't fit into place.
I'm secretly hoping the mandarin turns out to be a fake-out. He really was the mandarin playing an actor when needed to escape, and showing up in a later movie. But I'm not too hopeful about it.
As far as the panic attacks, PTSD isn't a binary switch that's either on or off, and that can only come from one really bad experience, and happens immediately after the trauma. Tony's been through a lot starting with the first movie, and has steadfastly refused any sort of therapy. It's going to catch up to him, and it did. It didn't have to be solely the events of the last movie, it's likely the combination of events over the last several years of his life.