How much tachycardia is normal when standing? Do I have POTS?

I am a 36 year old male. I have lightheadedness and dizziness that happens when I stand up after lying down. At first I thought it might be orthostatic hypotension and I started taking my blood pressure and pulse before and after I got up.

The blood pressure actually goes up slightly. I feel my heart racing and pounding in my chest when I get up though. On the 7 times I checked it, my pulse went up 32, 46, 38, 44, 49, 34, and 31 beats immediately from lying down to standing.

The pulse increase of greater than 30 beats only lasts for the first 2 minutes or so, but then it starts dropping below the 30 extra beats after that. Within 5-10 minutes, I feel a little less dizzy and the pulse is about 15-20 beats higher than lying down.

Question 1: Is a 30 to 50 beat increase in pulse a normal response to standing up or do I have POTS (Postural Orthostatic Tachycardia Syndrome) or something else?

Question 2: If this is not normal, what other conditions besides POTS could cause a rise in the pulse like this?

Question 3: Does the 30+ increase in pulse have to be sustained for more than 2 minutes for a POTS diagnosis?

Please help! Thank you for your time.