I suffered from a similar situation when I was working. When I started to feel overwhelmed I usually went into the ladies' room and into the handicap accessible stall and I would try to just breathe, taking deep breaths. As I inhaled I would try to count to 10 and count to 10 again as I exhaled. I would also try to stretch. My bouts were due to overwhelming anxiety. There were days I probably spent more time in the ladies room than I did at my desk. When I was in a situation where I couldn't get to the ladies room I would quietly do my breathing.
Other times I would inhale and picture the exhale starting at the top of my head, working its way down, taking all the crap with it and out through my toes. After doing this a few times I would start to feel my body relax.