This is a tough one, obviously. You don't want to be passed over, but if you don't make your company aware of your illness then you have no recourse if they let you go for being sick.... I think, personally, you just do what you can going forward and if you have to start taking time off, you start documenting with your doctor and your boss. Heaven forbid but if you should eventually end up disabled, the records of your lessening work will really help...
Wishing you well...

Yes, Nina offers very good advice. There are laws that employers have to follow when an employee becomes disabled, they have to show that they've made efforts to accomodated your limitations. I did not know this when I stopped working. Hopefully you'll be able to continue to work as long as you wish, but it's a good idea to be prepared and you need to be honest with your employer. It's better they know you have good reason than that they think you're slacking off.

Askjan.org has great info on the Americans with disability act. I have asked for a few accommodations in my job. I have not told my school district the severity of my health issues or the brain fog but being a second grade tea he I have asked for no recess duty. I frequently am unable to stand for the length of time needed. I decided I didn't want A lawsuit because I was sitting while some suing hungry parent's child was hurt at recess.

If you need help ask. My dr said to be very careful in asking for accommodations he suggested to put in writing so that your wordage was exact. You don't want to tell too much. My dr helped me word the letter. That way I wasn't putting my job in jeopardy or hurting my chances for disability later on if I couldn't work at some time in the future. I'm scraping buy with the health/ medical balance right now but you never know what the future will bring.

This is a tricky one. I have a management job as well and I try really hard to do a good job, not doing as well as I would want to but still pretty competent relative to other managers.

I have taken the full disclosure approach so my boss and folks around me know what is happening. I think sometimes that given a do-over I would take a different approach.

CFS is a nonsense diagnosis. Even if you provide information and people do research they will tend to dismiss your illness. Have you ever heard the phrase 'a little knowledge is dangerous?'. Folks have used bits and pieces of CFS knowledge against me, like the brain fog. Insisting that I am forgetting stuff or not recording things straight, having written records has validated my position on some occasions but it really does not change the overall perception.

I think it does affect long term decisions such as promotion, so if I had to do it over, I would not discuss it.

PS : I agree with others that you should let your boss know you are having health issues and the impact of those on your work schedule, mobility etc. The specific diagnosis of CFS is the part I would keep to myself.

Update : I spoke to my boss yesterday about my upcoming surgery. I have no choice, I will need extended time off. I expressed my concerns re the after effects and the possibility that I may be in hospital longer than normal.

She brushes aside my concerns indicating that she did the same surgery with no issues. I said "well, you were healthy, I am not" and my boss says
"It seems you are looking for excuses to be sick .. ARE YOU SURE YOU ARE NOT A HYPOCHODRIACH?"

Even today I am still pissed. As I said, the less said about the CFS issue, the better.

MaxPB that's the way big company's do it.You are just a number to them. I think it's to hard to explain CFS and fibro to them. For many people if they don't see blood or a bones sticking out it's not real.This is what I'm afraid of and that fact many people just think your being lazy.With all these good post coming in I still don't know how to handle work and fibro and CFS???
Good luck MaxPB keep in touch.