@avarj I got the exact same impressions from both Dr. Nakaji and Dr. Lawton.
My symptoms started VERY abruptly after three 50k IU megadoses of vitamin D2. As in, I went from no symptoms (besides a syncopal episode every 8-12 months) to having all these new symptoms (head pressure, lightheadedness, etc) in the span of three weeks. Permanently.
Every single doctor I have told this to has no idea what to do with it. A few have told me it’s downright IMPOSSIBLE for vitamin D to do this. One of the doctors who told me that was an endocrinologist!
When I told this to Dr. Nakaji, he was similarly perplexed BUT he did say there is a condition called hypervitamonosis that they see sometimes with vitamin A. He said a polar bear liver has a life time supply of vitamin A and has caused people issues when they consume it. Vitamin A and D are both fat soluble so it is possible they could cause a similar issue. He made it clear this was entirely speculation but he was the only doctor to both not deny the possibility and offer a potential explanation!
@Bay I recommend you read through my introductory thread here.
Ideally, I think you should get a dynamic CT Venogram with contrast. The imaging centers near me were very reluctant to do the “dynamic” part. I ended up drafting instructions with AI and giving them to the radiologist. (I actually lied and told them they came from my neurologist 
).
I would ask for imaging in as many positions as they can do. Both neutral and head turned in both directions. I would go on to have another exam (the angiogram and Venogram with manometry mentioned in this thread) that showed the most occlusion when my head was in flexion (chin to chest). That was NOT the position that personally seemed to make my symptoms worse so don’t just ask for the position that seems to make it worse.
This is the imaging Dr. Nakaji is asking for. If the imaging suggests you could have IJV, he will likely refer you for the procedure I mentioned at the top (angiogram + venogram with manometry).
About the insurance, as I mentioned, even if Dr. Nakaji is out of network for you, his team makes sure you are only billed as if you ARE IN NETWORK. It’s complicated but don’t eliminate him just because he is out of network! His surgery scheduler, Nancy, explained it to me.
Also, as just some general advice, don’t wait around for doctors office’s to do anything. Hound your doctor’s office until the CTV is ordered. Once it is ordered, don’t wait for the imagining center to call you. Call them and tell them you need to book it. After the imaging, don’t leave right away, ask them for the disk with the imaging so you can take it with you. Then you are in full control. You can send the images anywhere you need yourself without waiting on doctors to send it. (I wish I had done that with my angiogram but I was still doped up from the procedure and forgot.)
You will lose weeks at a time waiting for doctors offices to do things.