Yes definitely some people have symptoms increase when turning head to the side, or looking up or down. These movements can cause the veins to be more pinched by bone or muscles.
I have a pet theory that jugular vein compression may cause pots (one possible explanation: the body senses the constriction and pumps out loads of vasodilation signals, causing poor venous return to the heart from legs, abdomen etc. and therefore pots) but there's no evidence for this currently! That's why I'm so interested by the very early research showing possible links between iliac and abdominal venous compression and pots.
That reminds me of a post I saw on another forum from a young woman in the UK who fainted every time she lifted her head / looked up. She had been trying to get help but was eventually just told to “live with it”, i.e. try to never look up again. I hope she has found her way to the Facebook group you mentioned.
Is Doppler ultrasound any help in these conditions, e.g. getting the patient to move their neck in various ways and seeing whether the blood flow changes? I know it can be done on the arteries in the neck and the head. I suppose you would need to measure them simultaneously to try to pinpoint where the compression is taking place.
Or perhaps the new Lumia gadget that measures cerebral blood flow in an artery behind the left ear will reveal something. It is only a “health wearable” at the moment, taking measurements at intervals and giving a trend to display on a smartphone, but the inventors have plans to develop a medical version. That is still some years off but the company has formed good links with researchers and it all looks promising.