The MRI is a loud piece of diagnostic machinery. They will give you hearing protection when inside and yes, you must remain still. If you are claustrophobic you will most definitely have issues. Usually your physician would prescribe you a sedative for the procedure, because the physician who set the MRI up doesn't know the meds you are on.
If you don't have a sedative, a piece of advice if you find this difficult. Close your eyes before going into the machine. You lay on a platform that moves into the machine. Don't focus on the noise, it is loud, but use it as white noise. Focus your brain on a task. Count and picture the numbers in your head. Do the times tables, recite the periodic table, count to one thousand, by fives, count to one hundred by twos and simultaneously backwards from 100 by twos...you get the picture. The process takes about 15-20 mins usually and before you know it you're done.
Good luck, I hope this is all for naught.