Hey my friend!
Sorry to hear about these headaches!

I hope you'll get feedback to your question, because it's a goood one!
I'm still too much of a 'newb' with my SCS to feel qualified to give good feedback (5 months with my lumbar)....
I know you've had yours for awhile now......did these headaches recently start, or have they been going on for awhile?

My first thought leans towards wondering if your cervical unit being on for a long time maybe provokes some sort of slow CSF leak?
Especially since you say the headache dies down after the unit has been turned off for awhile.

Prayin 4 Answers
Rae