I do wonder whether something in the fitness lifestyle is a trigger. I was doing intense resistance training 3x a week when mine hit me. But another possibility for me, and for some others, are those protein shakes you mention. I was definitely sucking down a lot of those too. Protein powder has come up as a conjecture several times here or on Neuromuscular. Some possible connection between branched chain aminos and glutamate physiology. And even some speculation in the literature. So... careful.
Actually I say that more to prevent future anxiety and emotional distress then because I think it really is a cause. I wouldn't lay anything even close to even odds on any of the possibilities we've all thought of so far. Still, it has to to be something (or three). MS*t p** maybe.
