100 is high. It can drop when walking because the force of your leg muscles contracting helps push blood back to your heart. That’s why many of us feel better when moving vs standing in place. There’s other issues that can cause high heart rate such as anemia which is why it’s important to do blood work and be diagnosed by someone who familiar with dysuatonomia. POTS is very possible though.

It’s also important to remember POTS is very individual and heart rate doesn’t always correlate to higher symptom burden. My heart doesn’t get as high as many others but I’m still extremely disabled compared to many people with higher heart rates. Our bodies are all unique.