Hi
Over the last year at least I've been getting very quick split-second blackouts. I'd be staring at my screen at work and then it would be as if my brain shut down completely (not just vision, I wouldn't be aware of my head moving at all) and then it'd realise my head was falling just a few centimetres later. I'd then feel very dizzy and disoriented and I'd have a very bad pulsing headache for about 10 seconds but then I'd be back to normal.
It happens once every few months and I've never experienced anything else like it. I don't take medication, my blood pressure has always been fine and I never experience headaches or migraines or temporary loss of vision.