I have worked for a company for 15 years in IT and have recently been put into the on-call rotation along with a couple other IT staff (others have not been put into the rotation). Part of the on-call duties is to periodically perform system updates overnight 1am to 5am. There was one individual that used to do this on their own but my manager wanted a couple of other staff to learn how to do this so it's not always just the one individual. I struggle with severe sleep issues for which I require several medications and a strict sleep schedule/routine along with severe anxiety particularly regarding sleep. My doctor has provided a note for me to provide to my employer indicating that I have a sleep disorder and working scheduled overnight shifts is harmful to my progress in this regard. I have discussed this with my manager and they were receptive, however I continue to be scheduled for these overnight updates and my manager has left it up to me that if I can't do it then I need to either call in sick or find someone else to cover for me. This causes me a great deal of stress as I will be anxious for weeks whenever I am scheduled for these overnight updates. It bothers me to think I need to come up with an excuse each time this happens. Is this something that I have no choice and will need to deal with or should I be meeting with HR and presenting them with the doctors note and request an accommodation? I'm worried that I will seem like a bother and they will find a way to push me out the door. What should my next step be?