In the short run your body is preparing itself for action. It is making you focus on the most important things.
As a result of this your brain will try and "automate" as much of the non-vital behavior as possible. This is not a bad thing; by nature we humans are creatures of habit.
You may see this automated stress behavior if you took the milk out twice this morning or if you are spinning a pencil in your hand while working.
Note: Smoking can also be short stress behavior, but it is not a healthy habit ;)
I like jumping my leg rapidly on my toes like a dog trying to scratch itself where it can't react. I say "like", but really, I have no control over it. But it is an indicator that I look for and when I observe the stressful behavior, I know I should look out for some of the more serious long term behavioral effects of stress...