the drop hit me 3 days later, what is going on

right so saturday night was honestly one of the best experiences we've had, full swap with a couple we'd met twice before, everyone was buzzing, group hug at the end, the works. monday i felt brilliant. tuesday slightly off. wednesday i was crying in the bath for no reason. my partner's like "are you ok" and i'm like idk?? i wasn't pressured into anything, nothing went wrong, i actually enjoyed every minute. is this what people mean by "the drop"? why does it hit me days later and not the morning after? feel a bit mental ngl