Probably wake up terrified. Walk around and enjoy it once I know what's going on. Masturbate (why miss the opportunity?) Take some NSFW photos of myself for when I'm myself again. Try and get in some same-sex... well, sex. Then, last minute, get a sex change operation back to what I was before the swap, so when the 72 hours are up I stay what I swapped to. Then when I really start to miss the sex I was at birth, switch back with another operation showing a selfie of my original self to the surgeon.