I also got massive FPS drops yesterday – from 60 FPS down to at times 8 but on average 20-30. If I disabled the Dugi guide in classic then the FPS returned to normal.
Using Titan Performance Issue the amount of memory used by the Dugi guide was increasing all of the time.
I disabled all add ons and tried out on a brand new character with just Dugi and was fine.
I then disabled Questie and went back in on an existing character and the FPS was fine also Dugi was no longer increasing memory usage all of the time.
My guess is that something changed in either (or both) Dugi and Questie and they are interacting with each other in way that causes the memory usage to snowball and as a result your FPS to tank (though I am by no means an expert).
But disabling Questie (which is not really essential anyway with the Dugi guide activated) seems to solve the issue.
BTW I am using the Mac client.