I can only tell you of my experience with it, everyone is different, some people are wheelchair bound, others can have mild symptoms (although, i can`t say what their symptoms would be like) For me, it happened after i had Glandular Fever. It took a while for Docs to find that in the first place, then a huge exhaustion hit me, not just exahaustion after too many hard days work,sleepless nights etc, it just crushed me, totally wiped me out. Even something as simple as blinking took all my energy that i had, i had never had anything like it before, i knew it wasn`t normal but i didn`t have a clue why i was like that. On top of the exhaustion, heavy body (everything felt like lead) i had swollen neck glands, every muscle in my body hurt, painful joints, muscle spasms..then depression kicked in. When you`re feeling like this 24 hrs a day, not knowing what`s happening, getting no answer from Docs, called a hypocondriac etc, no-where to turn..you just have to get on with it. Some days i finally managed to climb onto my bed, i then slept solid for 3 days, i`d wake up feeling quite a bit better, i`d be up and about, enjoying doing things again, thought i was `over it`..then it would hit me 10 times worse, back to square one again. You have to re-charge your batteries (so to speak)..but if you over-do things, you`re worse off than before.. So, you do have to pace yourself, and you do feel better at times, but the better parts are short..the bad parts last a lot longer..until things are back to normal, it`s impossible to work, you just haven`t got the energy.