Yes, that is perfectly normal (for panic). Happens to me all the time. We have these natural, inherant biological processes. When we are afraid (panic attacks) our bodies go through different motions. This was initially (for our long ago ancestors) to deal with danger from around them. But guess what....humans no longer need those cues because we are no longer threatened by predators and need to "fight" or "flight"(run away). At least for most of us, most of the time, ha! But really, it's just a biological process that is, like what was said earlier "harmless." Keep in mind several things - when we say heart "muscle" we are talking about a type of muscle entirel different than the skeletal muscles of, say, your arms or legs. The "cardiac" muscle is extremely dense and powerful, capable of maintaining a rate well over 200 for days and days without beginning to suffer any damage. Rest assured, this anxiety is a problem because it makes you feel a certain way...but that is all. Try not to focus on bodily sensations.