Hey, we've talked before.
At least its something to try, and a possibility.
On my adventure to get my eventual diagnoses of migraine, they actually thought I had something called Idiopathic Intracranial Hypertension, increased intracranial pressure for no apparent reason because all my scans were clean. My Neurologist thought he saw swelling in the nerve behind my eye, which was a sign for this. So they wanted to do a spinal tap to check the pressure, and to run a couple tests while they could.
So I got a spinal tap about two years ago now, now granted I don't have as many health issues as you do, so it might not be the same. The procedure itself went well, the staff doing it were great. I wouldn't say its a horrible thing to go through, there is like a moment of discomfort, but then its okay and tolerable. Though I'm not in a hurry to do it again. But mine actually did relive my pain for about 24 hours
I found the hardest part for me, is the for the first 24 hours afterwards, they want you laying down as much as possible. And then I pushed myself a bit after that, and I think that is what led to me needing a blood patch, I got spinal headaches (Which were worse than my migraines! And that is saying something!) The actual procedure for the blood patch is SO SO SO much easier than a spinal tap, so for the record if you do end up needing one (And hopefully you don't) it really isn't a big deal. Its like getting a shot, its quick. You have to stay laying for a bit, but if its what you need, it helps right away.
The best thing to do, is to really try your best to think positively, focus on the good. That this COULD help with a diagnoses, at the very least it will rule things out, it could help with the pain (which is greatly needed). Focus on those things, and don't let the fears get to you. Because if you do, you'll only freak out more than you need too. I know before my own spinal tap, I was freaking out the entire week before, and I realized afterwards I really didn't need to.
So hang in there, think of positive things. If you have any questions, let me know.