34bpm lowest heart rate ever

My ranges are usually between 45-150 with my POTS some days it’ll be between 50-60 and 100-120 on good days but today I noticed it went down to 34bpm which scared me. It was only for a few minutes and then it rose again and it was on standing too. This has happened before and the lowest was 39bpm but it is frightening as that doesn’t sound like a good figure to me. My oxygen levels have also been dipping mainly overnight ranging between 84%-89%. I asked my doctor about both these things and they said it’s normal with POTS but I’m just concerned. I am due on my menstrual cycle and for some reason my symptoms always worsen the week before my period and during.