Well, from what I've read, and from what I've been told (by a doctor) they're one in the same, and completely different.
The doctor I spoke who specializes in just CFS/FM, said that in his research, CFS/FM stems from a virus/infection.
In research that I've done, and reading Dr. Wilson's book (based on Adrenal Fatigue), he's said that's brought on by stress. Now, stress can come from infections, physical injury, emotional....... You can stress about anything really. I "believe" Most of the world is stressed about something, and never know it. I didn't know I was stressed. I thought I had some worries, but didn't hit me until I really looked back and said... "Wow.... I was really stressed about that".
Just to give you an example. I was coming home from my accountants office with my Wife. We were just told that due to a tax screw up on my paychecks, we would owe the IRS $4,300 this year. Now, we were already strapped for cash, being that we just bought the house 6 months prior, just got married 3 months prior, I just got into a car accident (wasn't my fault, but it was totaled), and just changed jobs.... I remember going home after that, freaking out, yelling at myself, then getting into a fight with my wife, then deciding to workout. I remember while running (my basic run was 4 miles) that night, thinking about how I was going to pay that off. How was I going to make end meet. Before I knew it... it was raining, and according to my wife, I was gone for over an hour. I must have ran atleast 6-7 miles that night. I remember my heart racing, I remember my adrenaline being through the roof, because I was pissed. I was using my anger as energy to run faster..... this is what I did for months, and well.... it caught up with me.
Personally, I think anyone questioning about the Two should atleast consider spending the money for a saliva test. Almost (and I say almost based off what I've read, and experiance) all doctors of western medicince will not do a saliva test kit, nor will insurance pay for it. They will however, laugh at you and tell you that they 8-10 years they spent in medical school didn't tell them about this, except in Addisons/cushings disease.