I don't mind at all. I have to stay alert for the pancreas since I have to hold my breath at one point, but all I do for the brain/spinal cord is lay still. The machine vibrates, headphones dull the sound, and sometimes there is music. I could sleep and I find the vibration kind of soothing - much like being in a car.
I kinda look forward to it, honestly.
It is possible to sort of sleep on psychs. I guess it's not quite sleep; it's more like a relaxed state of altered consciousness within the "normal" state of altered consciousness. I sometimes become alert again and realize I dozed off for a few minutes without losing track of time.
I can sit there with my eyes closed while on LSD. Same with mushrooms. Mushrooms are a bit more fun with that because of the visuals and patterns - I've spent some hours like this in a hotel in Amsterdam (truffles, obviously).
I already find an MRI relaxing - they give you a button in case anything goes wrong, after all, and they can put music in the headphones. I can definitely just relax there and I can definitely see how it would be pretty immersive. Plus, I'm pretty sure they aren't giving these folks contrast through an IV and that's really the bit I'd have some issues with.