Racing heart standing - normal?

I have a wierd symptom with my heart, which I had always attributed to GERD, however now I am not sure as it happens absolutely every time I stand up, no matter whether my stomach is empty/full or w/e.

My resting heart rate when lying down is very low, when Im flat and totaly relaxed its about 50, I recently had an MRI and it took forever because they said my breathing couldnt be detected by the machine, I was hardly breathing at all but this is normal for me. But when Im seated its about 80-90bpm, and then when I stand up and stay stationary I feel pressure in my chest and my heart races at about 130bpm. This doesn't go away, the longer I stand stationary the worse I feel, I start to feel nauseous. Strangely it is better when I walk around.

I've had my blood pressure checked frequently (when seated) and its always been normal.

Recently I have begun almost fainting whenever I go from lying down relaxed to standing up. I have been eating less due to stomach problems and always put it down to that, but surely that isnt normal for it to happen EVERY time I stand, and its not like Im starving, just eating less than usual.

Does anyone else have these symptoms? Should I go see the dr about it?

100% see a doctor as Alice suggested.

But when i had acid reflux, i was getting racing heart every time i stood up or moved to go as somewhere as simple as the toilet. I was breathing rapidly and felt i was getting no oxygen when sitting down normally. I have had very strange symptoms with gastritis when it first started affecting my breathing 1 year ago and when it got worse after Christmas and also when it got much worse 3 months ago. Its always effected my breathing but the symptoms are strange to say the least, no 2 days the same. I did find things would get better if i took Galveston with food, my breathing would improve somewhat and sometimes not. So might be worth a try if you don't have any medical issues o take Galveston.

but go and see a specialist cardiologist and make sure your ok.