It's your brain releasing extra neurotransmitters.
When people drink a lot, their brain compensates for the depressive effects of alcohol by consistently releasing more GABA - an excitatory neurotransmitter. When you quit drinking, your brain still produces the excess GABA, often for a long time. The brain takes awhile to calm down. GABA's role is literally to pump you up. That's why newly sober people are so worked up, anxious, tense, nervous, restless, etc.
There are other things going in with you chemically that are part of the body's biochemistry of addiction. You can google "biochemistry of alcoholism" if you are good at the internets. I also recommend reading "Beyond the Influence - Understanding and defeating alcoholism." I enjoyed it and learned a lot.
Alternately, there are spiritual, emotional, and mental explanations for what you are feeling. None is necessarily better than the other if they help you out.
Good luck.