Good afternoon Cogito!
...I really don't know, but it seems like you have a possible handle on what may be causing it. Is there a chance they can switch you back over to oxycodnone..and see if the same symptom shows up?
It could be tied to teeth problems and or a slight case if TMJ as well...and you say it comes on at the end of your med cycle.
It's interesting, and I hope you find the cause, and a simple solution can be implemented to cure it. Headache's can be hard to deal with, and send a person straight to bed.
Moderator Chronic Pain Forum
Weekly Quote! "Getting over a painful experience is much like crossing monkey bars. You have to let go at some point in order to move forward."