Hello Ali,
Whenever people ask a question like this, with no clear answer, I look to the literature that is available.

As you can see above, Amanda sent links to articles about how people can get new or worsening POTS from a Covid infection. It is a common enough post-Covid occurrence that clinics and practices that treat "long Covid" patients have specific treatment protocols for it.

Reading of your acquaintance's unfortunate side effect from the vaccine, I looked to the VAERS data (Vaccine Adverse Event Reporting System https://wonder.cdc.gov/controller/datarequest/D8 ) where you can search for every reported instance of a side effect thought to be the result of the vaccine. Citizens can report if they wish, medical providers are mandated to report these events to VAERS.

Here is what I found:
434,000 events have been reported of the 350,000,000 doses of vaccine.
91 have mentioned POTS as the symptom
54 hospitalizations and 0 deaths were reported
1,000,000 people in the US have POTS

That means:
2 in 10,000 (.0002%) who have a reaction report POTS or 3 doses in one million (.000003%) result in a POTS reaction.
1,000,000 people have POTS in the US, about 3 people per 1000 (.003%) in the US have POTS, using the numbers, it's possible you would have a 1/1000 (.001%) chance of SOME reaction to the vaccine.
1/9 (11%) of people have gotten Covid.
I don't know how many people who actually reported POTS after a Covid infection, but to be part of the post-Covid rehab protocol, it would have to be significantly more than 90 people.

So I believe you can safely conclude that getting the vaccine is a lot safer than risking getting Covid, which tends to be more severe in people with underlying conditions.

I do not have POTS, but I do have underlying health conditions. I knew I had a high chance of inflammatory reaction to the vaccine, but chose to be vaccinated anyway. I got a severe reaction, was treated (in my case they used steroids to control it) and am now fine. I will get boosters as recommended and my other vaccines, even though I know I will probably react again, to protect myself, my little grandchildren, and help stop the spread.

Does this help you to make your decision?

Sue