Hi there 🙂 I have the same issues, when I lay flat I start to feel sick, nausea, heart racing and bounding, headache. If I go further back than flat it gets so much worse. I am wondering since I have EDS and POTS if maybe there is a chari type issue going on? I have not been diagnosed with chari but I have also not have the tests for it. It my thoughts I can kinda see that laying back would either cause the spinal fluid not getting to the brain to kind of back up or maybe the pressure is taken off the brain a bit too fast I dont know, I am not a doctor just thinking maybe it works this way????? I kinda feel a bit of a paralyzed feeling but its slight its more the other symptoms and it takes me a very long time, like hrs and meds to feel better. I have many many other issues as well, like chronic everyday headaches, I live on norco for this. My heart and blood pressure are very unstable as in highs and lows. Alot of neck pain and joint pain. Sleep problems and so many other things its hard to list them all but the good thing is I see a great doctor in ohio who specializes in POTS named Dr. Grubb. He is with the university of toledo heart and vascular center. I am going to mention all of this to him at my next appt and see if he can order a test for chari. BIG GENTLE HUGGGGGGSSSSSSS to all of my POTS/EDS/CHARI/or any other related disorders, prayers so research and a cure !!!!! <3