How common is a venomous snake bite on the AT and at shelters/camping areas?

Yesterday on the approach trail to Springer a rattlesnake was laying beside the trail in some grass. He didn't rattle until my foot went down inches from him. I've stepped right over snakes more than once because I never saw them, but Mr. Rattler left me concerned. It could have easily turned into a bite.

How common is a bite for a thru or section hiker? What should you do if bitten? I see only two choices: 1) Sit down, relax, and call for help, or 2) Walk to a road. This has been discussed at whiteblaze before but I never found satisfactory answers.