I can have a seizure at anytime or anywhere .Doesn’t matter , if I’m standing or sitting. They come out of the blue unpredictably.

Terribee, that's 100% what I'm talking about! Thanks! Yeah, I've been hurt quite seriously a few times. Hopefully you have a good support system around you. That makes a huge difference.

When laying down, and often when asleep the blood pressure is lower, as your heart is horizontal and we relax. upon standing up and moving around too quickly, the brain gets deprived of bloodflow, as the blood pressure has not increased to normal range and syncope happens. You pass out.
It has been happening to me for the last 5 years. Only preventative is to sit up in bed for a couple minutes before walking around.

There's also something called micturition syncope where you wake up in a hurry and have to visit the restroom to urinate. When finished, you pass out. Sounds funny, but it's serious. Mostly in men. Combined with getting up from horizontal position too fast, relieving the bladder also drops flood pressure and can result in passing out.
No cure except to 1) get out of bed slowly
2) sit down on the potty.
Sorry to be blunt.

Do you seize? Only know if someone witnesses.

I used to think I was fainting

Yes, I get out of bed and black out and fall down for a minute