I went for what i think (if i recall correctly) was an MRI of the brain at around 15 as i suffered from migraines. They ran in the family, and i had been getting them on and off for years.
I can see why people find it all a bit daunting - the room was cold and simly lit, you laid back on a platform that slid into what could best be described as a massive washing machine, and the contact you had with the nurse & operator was through an intercom.
I can distinctly remember the only thing that bothered me was that although i was saying "erm hello - there is a hot wet feeling in my ear" as i could feel a very hot wet feeling that could have been sweat but at the time felt like it might have been blood

Makes me think i was a drama queen - but at the time i felt more frustrated at nobody replying than i did at it happening. After all i was in good hands.
The lamest part was all the "did they find anything" comments when i got back to school.
I'd suggest that you go and see your GP if you have any concerns.
For me in the end i needed to do some eye training exercises and it minimised the problems with migraines, albeit not completely.