Breath! Commit to a sober today. And do it again tomorrow. Be patient with yourself. Don't go sprinting out of the gates. Start slow and steady, under control. Pace yourself.
"I am a slow walker, but I never walk back." - Abraham Lincoln
It is not the end of the world. Discard the failure mentality. Your goal is long-term sobriety. Get back on track and continue to plug away. Sometimes a lapse can serve to reinforce you path and goals. You may have an epiphany that using is not fun, not healthy, dreadful, and that you never want to be there again. It can also help you identify certain triggers/emotions that need attention.
"Never confuse a single defeat with a final defeat." - F. Scott Fitzgerald
Do absolutely everything that it takes. If it takes going to meetings everyday, then do it. Losing your health, your family, your career, and invariably your life, is drastic!
"It is not enough that we do our best; sometimes we must do what is required." - Winston S. Churchill