I understand that they routinely give a sedative beforehand to those who are claustrophobic. I think claustrophobia is quite common in people when the head is also inside the tube.

I had it done on one knee once, so most of my body was not inside. In my case the painful part came about because the technician, after cautioning me that if I moved any part of my body while the scan was in process she would have to begin over, she wasn't able to get it to 'set up'. She didn't tell me until almost a literal half hour had gone by. I had thought all the humming and clanking sounds meant that things were going swimmingly. Then she left the room to get a different 'cone'. Of course, she cautioned me not to move while she was gone.

My body was already uncomfortable, almost in pain, at this point and I was looking forward to just 15 more minutes of immobility. (It is surprising how painful it is to hold completely still; evidently we move and adjust position far more often than we're aware of.)

Anyway instead of 45 minutes the process took almost two hours. I was sore the whole next day, which had nothing to do with the MRI itself.