I have inflammatory arthritis and secondary fibromyalgia (and menieres) and am currently undergoing tests for possible lupus (malar rash, frequent infections and other things). Things have changed dramatically for me over the last few years especially, I can't imagine doing some of the jobs/hours I've done previously.
My employers have been great about the arthritis. I know what you mean about worrying about making a fuss, I had to have an occupational health review before being taken on direct (from agency) and I was quite defensive as I was worrying they would try and stop me getting the job direct but it was really helpful as it recommended things like a proper DSE assessment to make sure I was comfortable and rest breaks etc... It also said I would be likely to come under disability legislation with at least two conditions.
I have a variety of things to make things easier, a wrist rest and I use wrist supports when I need them, a document holder and they have helped make sure I get a comfortable chair I can adjust and I can get up and have rest breaks when I can move and stretch.
I'm encouraged to get people to help me when I need it (eg picking up heavy things or bending down) but I'm still rubbish at that but find people are only too happy to help when I do ask and some just do it automatically for me if they know I'm bad. I am pretty honest and open about things so people know what is going on. I find it helps people understand more as so many people just don't realise what some things entail, you mention arthritis and they think you have say one joint that hurts if you aggravate it rather than how it is.
I worry about potential time off as I've recently had time with an infected gallbladder, meaning a week in hospital, and then the operation and recovery itself and three days when the immunosuppressants I was on for my arthritis knocked me flat and made me ill. I feel awful about having any of it off, not that it could be helped, and it puts pressure on me if I needed any more. Luckily I have holidays to use and we have a flexitime system so I can work more when I'm not feeling so bad and have a shorter days or take a holiday for a shorter week (and like when I had a bad cold a couple of weeks ago) when I'm in a lot of pain or more exhausted.
There are possibilities such as part time working or job sharing but I just couldn't afford it, I struggle enough on the full time wage I'm on at the moment.
I try to book appointments I can (physio, blood screening, GP) really early or late to fit in with this so I don't have to take them as "leave" as such.
Another thought is asking your rhumatology department if they have services which could help. My one has patient education mornings and I'm trying to get on one where they have specialist nurses, physios and occupational therapists who give info and advice and so you can meet others with similar conditions.
Has your workplace expressed any concerns?