So, how did you get from chitchat to sex? I'm always curious about that first move.
It's explained very very clearly in OP's post, with the words "next thing I know". Happens to me ALL the time. One minute I'm in line at Duane Reade; then suddenly there's a blackout and when the next scene begins I'm being double-fisted right behind a stack of unopened cartons of Chex Mix and Pamprin.