I don't get full blown panic attacks, but I get extremely stressed out as well during tech interviews. I think I'm a pretty good coder/computer scientist - I've released tons of open source stuff, spoken at conferences, solved many Project Euler challenges, published papers, taught people how to code, etc - but my success rate is still abysmally slow in interviews because of that.
For me, it's a mix of the stress of feeling judged, having to "impress" someone in a very short timeframe solving a problem they know perfectly and that I have never seen before, the fact that I am naturally introverted and shy, etc.
A friend of mine who works at a large tech company in Seattle told me he took Xanax before his interviews. Another friend working for a big tech company in the valley told me he'd chug a couple beers before his. Yet another friend working for a fairly large "startup" in SF recommended that I smoke a joint before my interviews.
Our industry is weird.