12 and 13 hour shifts is a lot for anyone suffering from fatigue. Is there any way you can ask to split your shifts? I'm asking this because it's exactly what I had to do. I used to work longer shifts but I had a relapse and just couldn't keep it up. I was too tired, and my body wasn't getting enough chance to heal. When I explained everything to my manager, he was more than happy for me to split my shifts. I still do the same amount of hours but I work more days and shorter shifts. It's working for me. Maybe that could work for you? Ask your MS team for advice. My MS nurse has always told me that if there are any problems at work, someone from their team can go and speak to your employer to explain your situation and needs. It's not about sounding like a child. MS is hard enough without being made to feel like this about your work place. Your manager should understand.

@nakedandafraid , in the UK, we have legislation to try and protect us from bossy bosses, who don't understand. You need to research and see if you have any such protection in Ireland. This may be a good place to start, https://www.citizensinformation.ie/en/employment/employment_rights_and_conditions/ . The MS Society may be able to advise, https://www.ms-society.ie/ If you are a member of a Union, you should consult them for advice. You should not be hounded out of a job, but I can understand the reasons for looking for alternate employment. You shouldn't have to give a reason for leaving, but if it's for a job application, you could put "Poor work environment" and leave it at that.