gm techniques – Need some quick inspiration for a fae queen encounter aftermath

I’m looking for a bit of inspiration – the D&D party is about to encounter the fae queen, and the Faustian bargain she’s going to go for is going to involve “1 hour of time” from a specific person in the party.

The plan is to have them return, with no memory at all of what happened, and a few vague aftereffects – a wound on the shoulder, possessing a completely different weapon, or such. I’m looking for things with no obvious reasons/causes that can be open-ended and eventually play a plot hook later on down the line (plus, it’ll mess with their heads.)

Any ideas?