Yesterday evening (GMT) my reputation dropped from 6650 to 6218 all of a sudden. Why?
A couple of questions were deleted. I've undeleted them for the moment as there is nothing immediately obvious to indicate why they were deleted. If something is drawn to moderators’ attention, or otherwise comes to light, they may disappear again.
Those questions accounted for the majority of your loss, and you’re currently back to 6530.
We may be able to shed some light on what’s happened to the rest, but moderators don’t have access to a detailed history of reputation changes.