Yikes!
How much sleep have you been getting, Dave? Sleep deprivation is a well known cause of seizures, even in totally normal healthy young people. Considering that this happened completely without warning, and that you were out for a while (however long it took for the ambulance to get to you, load you up, take you to the hospital, unload you into the ER bed, and the doctor to come see you = 15 minutes at least), there's a good possibility this was a seizure. Other causes of seizures include low blood sugar, alcohol withdrawal, & other metabolic stresses, or structural lesions (things you might pick up on an MRI).
If it wasn't a seizure, the other major cause of sudden loss of consciousness is loss of circulation to the brain. This is generally a cardiovascular issue, and comes in 2 flavors: (1) benign (simple faints; though usually when people are about to faint they feel lightheaded/queasy for a few seconds beforehand, rather than losing consciousness suddenly and without warning; also, people are usually out for only brief periods with simple faints), and (2) bad. This is generally some kind of electrical arrhythmia, where the heart beats either too fast or too slow to pump blood effectively. This is sometimes why healthy athletes can suddenly drop dead. The workup to rule out such things includes electrical studies like an electrocardiogram (looking for things like prolonged intervals or aberrant conduction) or ambulatory heart rhythm monitoring (called a "Holter" study here in the US), structural studies (like an echocardiogram), and exercise studies (a stress test).
You may not need all these studies or any of these studies....but you *SHOULD* get evaluated by someone in addition to the ER visit. Don't be stubborn, eh? If you resist, we'll sic Chris on you!
The other important thing is: SLEEP!!! No more staying up in chat to greet the dawn your time, ok? Go to sleep by 11:30 pm (your time) at latest, so you can get a minimum of 7 hours.