What Causes Fainting When Stretching?

I once passed out in a post office with someone it like that was not fun

Stetching actually tightens all your veins and increases your blood pressure. Pots or orthodontic hypotension both revolve around the Vagas nerve which controls triggers for blood pressure. So when you stretch its trigging your nerve that backfires in its function and causes black out or feinting. ... fun fact for you. But it generally won't hurt you unless you fall on something. I mentally needed to understand the science of it all to be ok with it.

I have POTS and stretching is the most common trigger for passing out for me.