Hey Shanna! I'm in the process of quitting and I know what you mean - the wound-up tense anxious feeling that goes with quitting - it's a pain.
I know it sounds really simple, but focus on your breathing. A large part of feeling anxious and tense is the way you breathe and hold the muscles of your upper body - if you take long, focused deep breaths, and relax your shoulders and neck muscles, it really, really helps relieve the tension. You're basically fooling your brain into thinking you are relaxed!
Also, make sure you have something to do to relieve tension in your life - sports, computer games, ranting on the phone to a friend - make use of anything and everything you can to make sure you kick that tension in the backside. Excercise will help burn off a lot of the latent energy.
And don't worry, my comment is only one of the thousands of responses you are going to get here - you did the right thing by joining this site - everyone here is positive and supportive. Good luck! 🙂