Concerning BPM

Hi guys! I'm 15 and currently going through some medical things, wrote a whole post about it in a different subreddit, but many redditors thought I could have POTS, so I decided to do a mock test on myself (laying down for 10 minutes-checking pulse, standing up for 10 minutes-checking pulse every 2 minutes) and I noticed a big leap.

After 10 minutes of laying down my BPM ended up being 60, and once I stood up it went from 120, to 140, to 164 and it stayed around there for a bit until it went back down to 120 and that's where it was the last time I checked.

I was definitely experiencing symptoms of dizziness and unsteadiness throughout it, especially when it read 164. I'm not sure if this is worrying because of my age, but just wanted to get any thoughts or opinions.