Hello

I feel for you lol !! 

I would thought that under the discrimination law & especially if you are registered with a disability (as I would think ME is) then your manager has no ground to sack you

I hope that I am correct on this but why not see if a friend or family member can do a search on Google for you & see your rights in the work place as an ME sufferer or even speak to someone at the Citizen Advice bureau or drop them a line

If your manager is aware that you are suffering with ME & that you get certain entitlement & so forth then again not 100% sure

I hope that your manager will understand your circumstances & that you are doing your best under the circumstances

Best wishes & hope it goes well !!