He has admitted to doing it before. A few years ago he admitted that before he went before congress to talk about funding for parkinsons that he quit taking his medications beforehand so he would twitch more. I am trying to find his quote where he said this, but with the latest situation every google search just turns up Rush Limbaugh and him.
I personally don't see a problem with it though, someone who is on HIV meds is going to look alot healthier than someone w/o them for example, and if you are on the meds people may think your disease is minor and not take it as seriously. In fact, there are problems with rising HIV infections now because people figure 'if I get infected, I'll just take the pills. Other people do and they seem healthy.' People get a false sense of how dangerous or curable diseases are if you can temporarily treat them. But I don't know if he exaggerated his symptoms for this situation or not.
Michael J Fox is an inspiration though. He has a serious disease and instead of becoming a shut in who is ashamed of himself and mad at the world he is out in public fighting for tolerance and to make the world a better place. He is raising money, raising awareness, raising scientific funds. His foundation has funded 80 million dollars for parkinsons research so far. He could've just retired to his home and never left, constantly being pissed off and afraid people would laugh at him. He did the opposite though.