I want to point out that Orthostatic Hypotension is normal to some degree.

If you experience it changing positions while sitting, or notice exercise and heat intolerance, talk to a doctor. In the short term drink enough fluids and get a bunch of sodium and potassium in you.

Edit: Im going to step out here and say that I am personally familiar with a condition called Postural Orthostatic Tachycardia Syndrome. It's somewhat uncommon, and has a lot of potential causes. COVID-19, specifically, can trigger it because of the way it attacks the nervous system. However, the symptoms of POTS are also the symptoms of a BUNCH of other much more serious conditions. It's a diagnosis by ruling out other things. When they get to the step of testing for POTS it's hilariously easy. They monitor your heart rate and blood pressure, stick you on a moving table, and tilt you.

On the downside, POTS itself is incurable unless the underlying cause changes or improves. This happens in many people, I was unfortunate enough that they discovered I had unexplainable neuropathies. Either the nerves were damaged when I was young, or they didn't grow correctly.

The upside is that we can manage POTS symptoms. Avoid heat. Build lower body muscle, increase electrolyte intake, and drink a lot of non-caffinated and non-alcoholic liquids. I take salt pills, drink Pedialyte daily, and have a prescribed (and extremely cheap) medication. It still happens, but it's manageable, and I won't die from a head injury anymore.