UK diagnostic procedures

Hello, I’m sorry if this has been said so many times before. I have thoughts that I have POTS and HEDS as I am hyper mobile, suffer with joint pain, Bowel issues and vomiting etc. in regard to POTS i am unsure if I have it. I have been fainting irregularly for the last year. Always when I come from sitting to standing for prolonged periods. Also feel faint / light headed once sitting or laying from going on a walk etc. been to the G.P and they claimed it was anxiety. As I have been in a car accident recently due to being light headed. I have gone back to the G.P. They did a sitting 1 minute and standing 1 minute. Whilst checking my B.P and heart rate. Also stage G.P was speaking to me whilst this was happening so that messes with the BP monitor. As it was only a minute my heart rate went from 65 - 80 and she claimed that it was normal. I explained about the laying down 10 minutes and standing up 10 minutes procedure in which my heart rate went from 65 - 105. I can understand others heart rate is more significant and my symptoms are more mild but I am no longer able to stand up and shower. The warm water make me feel faint and my feet become red and pins and needles. What can I do next? I’m worried if I faint again I might hit my head and die etc? Thank you