It’s part of the general misconception that “bad headache” = migraine.
Poor Matt. Yes, he was a lunatic, but I think he was a genuine lunatic – mentally ill through no fault of his own. I don’t think he was faking his “migraine,” particularly the numbness in his hands. I think it was a symptom of his breakdown. I’ve had some very weird bodily sensations occur during times when the bipolar disorder was acting up. I’ve felt the same way all along about his weird facial expressions – that either his meds weren’t agreeing with him, or that he needed meds and wasn’t using them.
I think the producers smelled “crazy” all over poor Matt, and cast him for that reason. “Let’s take this guy! He’ll be even more fun than Aaron was once the pressure kicks in!”