Same boat, Change. I had 4 months, then fell; unlike you it wasn't a night I fell off, but a month. Poof; yet another month of my life disappeared to booze. I'm now only a week back into sobriety; hurts, but I did this to myself and take responsibility.
So get back up, Change. Relapse can happen, and sometimes it happens to us. Find out why, dig yourself out of the negative feelings you are probably experiencing concerning yourself, and resolve yourself to sobriety again.
You can do this. If you're not comfortable with counting days or thinking of this as a day 1, then don't; the only thing you need to do right now is find out what event/circumstance you weren't prepared for and that tricked you into drinking, and to make sure you clearly understand how not to allow it happen again. Sometimes we get rabbit-punched in recovery; catch your breath, and then get back up.
You've got it, Change!