Go to the GP, they will probably refer you to a neurologist.
While you wait for the neurologist appointment, make an optician appointment, just to rule out an ocular cause.
Opticians do a lot more than test sight, they also test eye health and can raise red flags for more serious things like tumors.
I understand that you're afraid, and that no reassurance from me will help, but if its any reassurance at all, I find visiting the optician to be pleasant... 9000x better than a smear test.
If you feel like that again, it's perfectly rational to go to A&E, losing (full) consciousness is serious. I'd be tempted to call 111 even now and expect then to send you to A&E.
There will be a long wait, but there's no better place to be (when you could be dangerously ill) than surrounded by doctors, even if you're just in the waiting room.
Of course it could be any number of non dangerous things, I had similar symptoms with migraines (lots of nerve and eye weirdness, no headache).