I fell asleep during my MRI, too. Freaked the poor technician out. She thought I'd had a heart attack. Because unlike you, I didn't wake up when I came out. I was SOUND asleep. She was shouting and shaking me.
There was a problem with one of the images, and she called a few hours later to say I might need to come back in. Would that be too much stress and anxiety for me, to have two MRIs in one day? I was like, "I was the one who fell asleep this morning." She replied, "So, not a problem, then."