Fainting while sitting during pregnancy

Has anyone ever experienced fainting while sitting during their pregnancy?

I have unfortunately experienced many dizzy spells and near-fainting episodes from the very beginning of my pregnancy up until now(24 weeks🥰).

However, A few weeks ago, I fully fainted at the DMV, while standing taking my written driver's exam. I went to the ER and came out with a mild concussion , neck sprain and tailbone pain. It was a very scarey experience, but little Sun was completely okay and I've been extra diligent in eating small meals frequently, sitting/laying down if I feel faint from standing too long and hydrating alot more(2.5-3.5 liters of water a day plus fresh fruits & veggies).

My OB believed everything to be okay after running blood work, EKGs, and blood pressure tests. Just normal blood volume increases so I try to be realy careful and do all that I can to prevent another episode.

Well, unfortunately yesterday morning, I was taking an Uber with my sister and started to feel the onset of the same symptoms as the DMV incident. I first felt short of breathe, next a cold sweat, ringing in my ears, blurred vision and then I blacked out. It took 3-4 hours for me to fully recover afterwards still having waves of the blackout symptoms.

Never had I ever fainted sitting down before. I had noticed a few times over the last 2 months where I would be sitting or even laying down and suddenly feel faint but my symptoms would never progress to me blacking out.

I luckily already had an appointment scheduled today and my doctor was very concerned after I explained the incident yesterday. We again ran regular EKG and blood pressure test and everything came back normal. We're scheduling some more indepth heart exams, but I just wanted to see if anyone else has ever had any similar experiences while pregnant?

I'm a long-time migraine sufferer and like to focus on holistic preventions so anytime I have something health related that feels out of my control it's very difficult to handle the emotions around it especially while pregnant.