Something is wrong with me, did I have a seizure?

Hi, I need to give you all some background information before you make a hypothesis as to whether or not I had a seizure. I am a male, sixteen years old, and very light if that information is helpful.

For a little less than a year, I've been having episodes of vertigo. I thought it was ok, though whenever I stand up after sitting for a while, I become extremely dizzy and disoriented, and in some instances, I can't see for a few minutes. This happens several times a day now, and these episodes have become more intense in the last few months. A few times, I've passed out as a result.

Last night, I had some friends over. We were playing video games, and I was feeling perfectly normal, until about 11:30 at night. At that time, I simply couldn't rememebr a damn thing, and my brain felt as if it had stopped working completely. I headed to bed several minutes later, and as I lay in bed drifting to sleep, the strangest of sounds nearly deafened me, and I lurched back involuntarily, and was helpless to myself. I had convulsed or something, but I can't describe the experience. It was frightening. I ended up falling asleep an hour later, hoping that I'd forget about the event in the morning.

Now, it's the morning after, and something still feels off. My memory is extremely foggy and hazy, and I've forgotten several very simple words. I'm scared. I should also note that my cousin recently passed away at the age of 25. He had a heart problem that had never identified, and had a seizure a few days before he died.