From a UK perspective, maybe the Action for ME or ME Association websites have useful guidance on there about how to approach employers about chronic fatigue. It's a struggle loads of people go through, and hopefully I've pointed you towards some actionable advice. Working with CF sucks!

Thank you. My contract withy current company ends in June; any tips for searching for a understanding company? I work from home UK based, which really helps, but looking for a unicorn in terms of jobs going forwards

Commenting to follow your post, because I'm experiencing the same. I think it so depends on the line manager, I work for a great organisation that have always helped me feel supported previously, but my current manager is really crap to me. Makes me feel like I'm being reprimanded for needing to take sick leave or anything I do slightly sub-par at work, I'm really really trying though, I wish she got that...

Could you get a note from your doctor explaining your need to rest periodically or be able to sit more while you work? I know I feel less exhausted and in pain on days when I get to rest more, and managers at least will have to accommodate medical advice

I've been prescribed Provigil/Modafinil. It really helps me. I can't believe I survived this long without it. They say eventually your body will get tolerant to it so it's not going to work forever, but I've used it for about 2 years. I started at 25% max dosage and now I'm at 75% max dosage. But I'm also overweight trying to lose weight. Idk if it will work better if I lose some weight.

Honestly medical marijuana Sativa or Hybrid strains to be exact.

The website askjan.org is mostly in relation to the ADA (US disability law) but I think you could find helpful info on it despite that. It gives very good suggestions on how to formally request accommodations (their individuals section) as well as lists potential accommodations you might need for a specific condition/illness (their A to Z section) plus explanations of why they might be needed, etc. among other things. I don't know anything about the system in the UK but I still hope this is helpful!