You need to get to a cardiologist!
I had something very similar, and after basically forcing my doctors to take it seriously, I was eventually diagnosed with a large Patent Foramen Ovale (PFO), which is quite common, but also with Platypnea-Orthodeoxia Syndrome, which is quite rare.
Basically, my heart rate and blood oxygen saturation (O2Sat) would be fine if I was lying down, but if I walked to the bathroom and back, made some lunch, or even just marched in place for 15 seconds, my heart rate would go between 100-150 BPM and my O2Sat would drop to 86-88%. But after lying down for a minute or less, everything was back to normal! (It got so bad that I had to lay down after showering before I could blow dry my hair. My blood pressure went from 115/65 to 172/60 in less than 1 year, and I’m even taking blood pressure medicine! How high would it be without the meds?!)
A bubble echo showed a possible PFO, but the cardiac catheterization (while flat on my back) showed nothing wrong. So I kept pressing the issue and had a TEE (echocardiogram with a tube down your throat; thankfully you’re asleep!)
I wouldn’t let them put me to sleep until I spoke with the cardiologist, since the doctor who found nothing wrong also did the referral. This doctor was fantastic! She thanked me for explaining my symptoms and prior tests to her; it gave her more info about what to look for...and she found the problem! I’d been on home oxygen for 5 years and nobody bothered to find the actual problem! She discovered that ONLY when my heart rate was elevated, venous blood was able to shunt to the left side of my heart, bypass my lungs, and recirculate through my system. That’s why my O2Sat would drop after my heart rate would rise.
Thankfully, just yesterday they were able to close the PFO through a catheter in my groin. (They were concerned that it was too large for the closure devices. If that hadn’t worked, I would have needed open heart surgery to see it closed.)
But after less than 24 hours, although I’m a bit sore, I’m completely off oxygen! I got out of breath after getting out of bed to answer the front door, so I checked my HR & O2Sat....HR 78 and O2 didn’t drop below 94%!
Long story short, I recommend trying to print your stats from your watch (or start writing them down with the date, time, what you’re doing & how you feel), then get a referral to a cardiologist and take that info with you.
I just developed palpitations last month...I am only 25,male,132 lbs