To amars: IANAD, but your symptoms sound very much like acute migraine with visual components and perhaps transient ischemic attack. See for example http://imigraine.net/migraine/basilarm.html. Have you been under a lot of stress or overworked lately? Probably harmless, but you might want to go see a doctor, if for no other reason than to get some good painkillers in case you get the same kind of headache again. Actually, any time you lose consciousness for any reason other than natural sleep it's probably a good idea to see a doctor.

I've had visual migraines myself, with weird flickering effects in the corners of my vision and lost visual field, but I've never passed out or been nauseous.

Please take care of yourself.