Heart rate decreases after standing for a while?

I’m currently investigating if POTS might actually be what’s going on wth me. I’ve been feeling really faint and fatigued for the last few months and just the other day I actually passed out for the first time. I was lying down and went to stand up and then it happened. That kind of freaked me out as I’ve never had that happened before. So I did what I think I have read on this sub before as the “poor man’s tilt table.” Just so I have something to show to my doctor. I would really appreciate your opinion on it first though because I don’t want to bring it up if my symptoms actually aren’t a match for POTS.

I lied down for ten minutes and my HR was 70. I stood up and right away, and it went up to 135. I felt like I was going to pass out. After a minute it started going down a bit. The whole ten minutes I was standing after it kept jumping around going from as high as 120 to as low as 105. For example after 2 minutes it was 120. At 4 it was 105. At 5 it was 120 again. I’m wondering if this is because I couldn’t stand still without swaying? Can it be POTS even if my heart rate doesn’t stay the same after my initial standing?