Understanding Seizures/Epilepsy

Hello,

I have a couple of questions about seizures and epilepsy. I have mononucleosis, and recently due to being in bed for so long and walking around too quickly I passed out. While I was out I jerked around a bit but had none of the other symptoms of seizures. I was only out for 20 seconds and woke up to an instant recovery. In the ER, doctors told me it wasn't a seizure, I passed out and since I wasn't laid down, my body jerked as an attempt to get blood to my brain. They conducted an ECG and blood work, and a physical exam, all normal. They sent me to a neurologist as a precaution, he took my blood pressure upon standing and it dropped when I stood, so he told me that the cause of this was dehydration. He also told me that it WAS a seizure, technically. He sent me in for an EEG to check. The technician who had alot of knowledge of seizures told me what really happens, and assured me that what happened to me was not one. As she was conducting the test she told me that everything looks normal. The neurologist read it and called in telling me I don't have evidence of seizure activity.

Does this mean that my episode was actually a faint, not a seizure? What does an EEG tell? For some reason after being told by the neurologist that I had a seizure, I worry about epilepsy.

I am completely healthy, no personal or family history of seizures. I had never even fainted before mono. I have also never had any head trauma of any kind, and no infections. I don't have any tumors or anything like that. I am 18 years old.
So, basically my next question is, is it possible for a completely healthy person with no brain irritation or genetics to cause it develop epilepsy? Or generally are you born with it/develop it after trauma?

Thanks for your help
Katie