I am trying to find the verification on this but I read somewhere that the amounts listed on the posts, even though they say $, they are really steem. Hence, the value of steem doesnt affect the payoff, only the change in your total account value.

As for the drop, I notice that from time to time even though my tenure on here isnt that long. I guess it is the ebb and flow of the upvoting system. Perhaps some heavy hitters who were voting for you have gone on recess for a while.