Try meditation. I do it though not as regularly as I should, but it helps to calm you down. You start to notice more around you, mainly because you stop analyzing everything to the 'T'.
Read "The Power of Now" for a better (and lengthier) version of what I just said.
To add to this, there's several different kinds of mediation. The one you're looking for helps you relax your body in a way that doesn't fuzz your mind, or burns up your focus.
Some of the meditation methods overlap with deep breathing. You breath deeply by expanding both the bottom of the lungs, the sides of the lungs, and the top of the lungs. You make sure the bottom ribs are expanding. You don't try to force the expansion to the point where you're trying to hold air in like a puffed up balloon, greedy for more.
You cannot force yourself to relax. Consciously relaxing requires you to relinquish control over the muscles that are tensing up while still observing it.
In your case, I would also work on clenching and then relaxing your toes. There's connective and control tissues going from your feet to the jaws and temples.
If you're going to learn how to do this though, you'll need to set aside definite time where the startup cannot intrude. Supposing you set an alarm clock to buzz in fifteen minutes, then within the fifteen minutes of meditation/relaxation, you must allow all of the concerns, worries, thoughts, obsession, guilt with the startup to drift away. Otherwise, this won't work very well. There are people who develop superlative levels of skill in relaxation and meditation; these folks spend as much time and energy dedicated to it as you would to a startup ... so the least you can do is respect it during the fifteen minutes you are cultivating calmness.
I agree completely, except to mention that 15 minutes may not be sufficient at first. I wasn't even doing a startup, and 15 minutes was barely enough for me to let go for the first time I tried.
Very true. I experienced the same thing when I first practiced.
I didn't want to discourage anyone from picking up the practice, though. I wanted to point out it isn't a magic pill with an insta-cure, and it will take some time with daily effort before it starts working. Besides, the very first time, I had trouble sitting still for even five minutes.
Read "The Power of Now" for a better (and lengthier) version of what I just said.
And yeah, try and take it easy... :D