I have dizzy spells, my body shakes, feels as if someone is driving a knife into my brain

I have dizzy spells a lot if I don’t sit down immediately I’ll black out. My body shakes kinda like a seizure. I cannot control it. And nerves in my head tighten up like feels as if someone is driving a knife into my brain. I’m 23 I have got dizzy and blacked out in the past I think it started yet junior year of high school. But like my vision would be black but I could hear my self falling but couldn’t feel a thing what’s going on?