you could be experiencing a low grade panic attack. some ideas on dealing with the stress:
1 when you get home go for a walk it will help use up the adrenaline.
2 when you get tense eat an apple it will raise your blood sugar slowly and can have a calming effect.
3 go to the health food store and see the many products for stress relief. some really do work.
4 make a concerted effort to relax, once you have been runnig at warp speed for a period of time it can be hard to remember what relaxed feels like.