good luck with the MRI! I am glad that you like confined spaces, because I did not enjoy the feeling of being trapped in the MRI. (I didn't think I was claustrophobic, but I definitely felt so during the procedure!)
The hospital I went to provided me with a towel to put over my eyes and headphones for music, although paired with the loud noises, I found the music to be overstimulating. They even gave me a little oxygen tube to stick near my face. I guess feeling the air helped me feel less trapped.
I agree that the shaking was weird and unexpected.
I hope you have a good experience. Let us know how it goes.