I would research CSF leaks/Spontaneous Intracranial Hypotension as a possibility. People with hEDS are at an increased risk of having leaks. I have had, & still have multiple CSF leaks. I can hear them pop. I have at times also felt my brain move whether anyonr believes that
or not is irrelevant to me personally because a lot is not known about this condition still. POTS/dysautonomia can be comorbid with leaks. Orthostatic headaches (better after laying down for a period of time while getting worse the more time spent upright) are the most common symptom of having CSF leak(s). You mentioned feeling better after spending time in bed.
There is a csf leaker private group on Facebook where many leakers are more knowledgable than me. Dr. Ian Carroll has a few videos on youtube that are very helpful in explaining how hEDS patients are at an increased risk for leaks, as well as having POTS & other headache types as comorbidities. Best of luck & health to you.