FWIW, I have been diagnosed with ME/CFS and POTS for 3+ years and just started getting very similar sounding headaches occasionally after standing up from a sitting position in the past few days. First sounds began to pulsate, then a sudden splitting headache that only lasted a few minutes, then yesterday my vision became very blurry and spotty for a few hours. The vision loss was alarming, so I had a CT scan and no obvious problems were detected with my brain. Hopefully I will come to understand it better and how to avoid it. I'll try moving my limbs more before standing, in the vein of the posts here about going from lying to sitting before standing...