woke up the next morning in bed with the girl who invited me but my pants were still on, so. had a killer hangover too
I hope you don't mind some unsolicited advice, and forgive me if you already have done, but you should broach the subject with the girl you woke up to.
It may seem unlikely, but if you don't remember getting into bed with her then there's a non-zero chance that you may have had love and afterwards gotten dressed.
It might be a month on, but it's worth checking up with her and seeing what you both think, as well as asking each other about birth control and your loveual histories. Always better safe than sorry.