High heart rate standing up, worried about my health

Hi there, this is my first post and I'm not really sure how this works, also english isn't my first language, l'm sorry for any mistakes.

Two years ago my pulse was on the higher side (85-90 resting) but now its about 70 resting so I think it might have been due to stress and lack of sleep. I also did an ecg at the time which was normal except for a high heart rate.

However, about 1 and a half year ago i started experiencing heart palpitations every now and then (i still have them) and got a holter monitor for a day which apparently also came back normal. Despite that I noticed my pulse going from 70-80 up to 130-140 immediatly when standing up. In a few seconds it goes down to about 100 and stays at 95-110. I get dizzy and feel like im fainting if don't stand up really slowly. I also get blood pooling in my hands.

My blood pressure is on the lower side and I didn't experience these symptoms until last year, I think they might be related to a covid infection.

I also have horrible health anxiety which got worse after the palpilations started. I get high heart rates when im anxious but I'm sure the heart rate increase when standing up isnt caused by my anxiety as it increases every time when standing up even when I'm not anxious.

I spoke to three doctors and they all told me that it's normal but I don't feel „normal". They just said i need to exercise more and drink more water but I'm so scared to exercise but I go for walks every day and drink enough water. I'm worried that because of my anxiety l'm not really taken seriously.

I thought it might be pots but my heart rate doesn't stay 130-140 and I don't feel dizzy all the time. I measured with an Apple Watch last year but I'm so scared to measure again since it triggers my anxiety. Im scared of what it might be if it isnt pots.

Since my symptoms started i had 2 ecg's, a holter monitor for 24 hours, 3 bloodworks, 2 urine tests and an abdominal x ray. My blood pressure and pulse is checked reguarly. All came back normal except for palpitations and occasional tachycardia which I think is due to my anxiety.

I really don't know what to do anymore, my anxiety is being treated but I just cant get this out of my head. Currently I am in a psychiatric hospital and I can't consult any other doctors than my doctor here and she says it's nothing and won't examine me. I am aware that anxiety can cause all sorts of symptoms but this started before my anxiety got worse and won't get better unlike my other symptoms. I stopped checking my pulse but still feel like I'm about to faint when standing up. Should I try consulting a different doctor when I get out?