I blacked out today and I woke up on the ground shaking and this girl had to help me up I didn't…

I blacked out today and I woke up on the ground shaking and this girl had to help me up I didn't even remember falling all I remember is getting very dizzy and waking up on the ground. It always happens when I'm standing. When I opened my eyes and started to realize where I was and who I was, I noticed my body shaking uncontrollably and before it happened I got so dizzy that I lost my vision. This has happened twice before I got pregnant. Not sure what it could be. I eat normally & drink water everyday.