Chronic Fatigue Syndrome is not a matter of being tired in an ordinary way. It's sort of like gravity has been turned way up and it takes immense effort to move at all. Someone else described it as feeling like the air has turned to cement and you must push your way through it. A person I knew who had recovered from Guillian Barre syndrome told me she had felt the same way while recovering from that disease. The most similar feeling most people would experience might be if they go back to work before fully recovering from a bad case of flu, but that fatigue would be much milder than what people with CFS experience all the time.
I also had tender, swollen lymph nodes, aching muscles, and kept developing new allergies, mostly to foods.
After the first two bouts of mononucleosis my energy level averaged about 20% of normal. I discovered if I rested before getting to the tipping point of total exhaustion I could accomplish a lot more. For example if I could normally be up for about an hour before completely collapsing, I'd set the timer for 45 minutes and rest, doing absolutely nothing, for 15 minutes out of every hour. If I kept going as long as possible I'd be in bed for most of the day, but if I rested every hour before getting completely worn out I could be up a lot more total time during a day.
As I improved, the rest times gradually went from once every hour to once in several hours. I learned to tell when I was getting close to my limit and stop and rest before reaching it.
After a while I was usually able to work part time and would only be bed-ridden for a few days or maybe a week if I had pushed myself too hard, and that didn't happen often. That was back in the recession of the 1980s and my husband was out of work more often than not, so we were broke and even earning a little mattered a lot.