I call that a "physical reaction" to stress. I'm not complaining, really. But when I need to push through because I have committed to something, I look for a theme song.
My current theme song is "I Can Do This." It was written by David Osmond, son of Alan Osmond, nephew of Donnie and Marie. Both David and his father, Alan, have MS. David is currently working with Novartis (the national sponsor for this years MS Walks and maker of Gilenya) on a program called "Our Voice in Song" to raise awareness of relapsing-remitting Multiple Sclerosis. Check it out at http://www.ourvoiceinsong.com/info/david-osmond-ms-song.jsp
The words to I Can Do This resonate with me, especially the refrain, and has kept me going:
I can do this. Just take it one moment at a time. I can do this. Until the roller coaster ride comes to a stop, I can hang on.