Sudden random thoughts w/nausea...then unable to remember the thought. Help?

This has baffled me and my mom (I am 15). I don't know what is wrong.

Earlier this year is when it first happened. I'd be going about my day like normal, and then suddenly think of something totally random (and beyond my control). They wouldn't have anything to do with my life, things in the past, or the people around me. The random thoughts would be coupled with nausea to the point of almost throwing up. I never have thrown up, because as soon as I feel like I'm about to, the nausea and thoughts gradually disappear. It frusterates me when I can't remember what I was thinking about becuase that makes it hard to tell my mom what happened. The whole experience would last for about a minute.

After it stopped happening, I didn't think much of it. However, it happened again a couple weeks ago, then yesterday, and again today. The time it happens and what I was doing when it happened doesn't seem to be significant, for it differs. During and after it happens, I feel somewhat seperated..like I'm the only one there and it's hard to consentrate. That feeling goes away as well.

I have had some bad headaches as well, if that makes any difference. So, is this a symptom of something? Why is this happening?

Thank you for your time.