Thank you all so much for your response! 🙂
I couldn't find the said study anymore--probably I was just wrong and it doesn't exist at all!
@Pistol, thank you for the links! 😀 They were helpful nevertheless!
The surgery went very well, by the way! My anaesthesiologist went a couple of additional miles in addition to the one he had already gone before I posted my question here--he was extremely well informed, and I felt as safe as can be! He explained to me in detail why I should not get a lumbar anaesthesia (which I initially thought might work around the assumed postoperative exacerbation of POTS-symptoms), and he gave me additional fluids before everything started--just like Pistol recommended (but I didn't need to tell him!). And when he finally gave me the anaesthesia, he and his nurse held one of my hands and comforted me! Isn't that sweet?
When I woke up I felt really good! Also, my POTS-symptoms didn't get worse over the course of the week after the surgery! That took a lot off my mind! 😅