Recently diagnosed

You did too much so let's say you did 10mi s on the bike, wait until you feel good and do 5 mins. If you feel fine with 5 mins try at that level for a while and then SLOWLY increase. Using this approach in 18mths I can now cycle 30miles in 2hrs.

Best of luck

See if you can get a second opinion.  You might not have CFS, or you have had it fairly mildly, even though it's horrid.  Have a look around the web for some diagnostic criteria.  You could try 'SEID IOM'. and read through their stuff.  Also look up 'Invest in ME'.  Some doctors lump CFS together with ME.

For certain, if you have CFS, doing more exercise like you describe is wrong.  It's easy to do too much if you feel OK and then pay for it a day or two later, for a week or two.  

On this web page there are links to the ME association and others.  Spend some time on them.

Whatever you do, if it is CFS, be careful about what you do.  Loads of us have found, that unlike other maladies when a good workout can make you feel better, with CFS its the worst you can do.

On the other hand, being afraid to the extent of becoming inactivie is also bad news.  Find what you can do without 'boom and bust' or 'crash', do that, listen to your body.

Grrrr! Posts like yours make me so angry! You were given terrible information by your rheumatologist, assuming he meant exercise. If he just meant to keep moving, I'll give him the benefit of the doubt. Several years ago, when I was diagnosed, my rheumatologist had me go to the gym to exercise. That caused me to relapse. Right now, you need to rest, pace yourself, and stop exercising. Hopefully, you'll start feeling better. When you do, forget about the idea of doing exercise in the way you've done it before. Many researchers in the field hugely question the concept of graded exercise for ME/CFS patients. I agree with them, per my own experience. I'd advise you to do very minimal stuff and see how you feel. Maybe some yoga. Some very short walks. Back off if you have any problems, increased fatigue, etc. This is a bit hard to figure out because post-exertional fatigue can come as much as a week after the exertion. If you are in the UK, many in the medical field are following a protocol of graded exercise and cognitive behavioral therapy (CBT). Again, this regimen is hugely questioned by many experts in the field. If indeed your doctor has recommended exercise, I'd get another doctor. A specialist in chronic fatigue syndrome would be best--typically an infectious disease doctor. Doing a Google search on ME and CFS can yield some good information, if you go to reputable websites. Do a Google search on the "solve ME/CFS initiative," a website here in the U.S. that has lots of good information. 

I'd just just do what you find works best for you. Unfortunately there's a lot of quackery and nonsense around CFS, and lots of doctors think that they know more than they do. It's quite possible that you'd found the optimal level of activity for yourself.

People in the medical profession still dont understand ME/CFS i have had it for 7 years and now i have learnt that if i do something i will pay the next few days so you have to weigh it up, if you want to exercise do it gently walking the dog is good if not to far i am lucky as my dog is ball mad so i sit on the chair and wear him out that way perfect.