1) I've seen and treated patients with depression and they react differently to exertion. In fact getting out, doing things, and exercising helps with their symptoms. They may not want to go out but when they do, they often feel better.
2) Look at the section in Chapter 4 on PEM. The type of symptoms, onset, and duration of them in response to exertion are not like what is seen in depression. Most people with only depression do not suffer symptoms of pain, fatigue, etc. that last hours or days after minor exertion.
3) I don't think the line between "primary" and "secondary" depression is as clear as people like to think it is, especially for people with this illness and depression. Depression actually comes in many flavors. People may become depressed because they lost their job, their spouse left them, they are alone, etc. but they can also become depressed because of inflammation in the brain (what those who tout ME believe) or body. The strongest evidence has come from studies showing medicines that decrease brain inflammation can treat some depression that is non-responsive to traditional anti-depressants. (A blood test was used to show inflammation) Sick people could have depression due to both these causes. The science is not yet refined enough that we can say it was only the circumstantial reasons or it was only the illness.
While I used to think it was important to exclude people with depression from diagnostic criteria -- I don't have depression and I did not want them clouding studies -- my reading has changed my mind. *Including* people who are ill and have active depression may in fact provide a key to this illness: perhaps these are the folks with the most brain inflammation and by excluding them, we have or will miss the boat. The second key is to compare the folks with illness + depression with those that have illness but NO depression, not cut out people with depression across the board.
4) From a clinical point, there is NO science to say that if you have a psychiatric condition, you can't have this illness. That was a byproduct of Fukuda in my view because fatigue, not PEM, was the focus and fatigue is common in both depression and ME/CFS. There are no studies to show that being depressed protects you against getting ME/CFS.
There are likely people right now who have both illnesses but aren't getting diagnosed or treated for ME/CFS, even if they have it, because of prior exclusive criteria. How would you like to be one of those people?
5) Questionnaires will have to be developed or validated to address PEM in clinics but that is separate from the issue of listening and believing what people tell you, even with psychiatric conditions. People with psychotic disorders -- if they are treated, during certain times in their illness, etc. -- can still communicate their symptoms accurately. I had schizophrenic patients on regular medication; they didn't have any problems communicating and I didn't have problems understanding them. Similarly, I had patients with Alzheimer's disease whose complaints were dismissed by other doctors -- the assumption was they don't know what they're talking about -- but many did if one took the time to ask and listen. Assessing someone to see if they are actively psychotic and unable to differentiate reality from hallucinations is different from an across-the-board view that mentally ill individuals can't realistically convey their symptoms. We want healthcare professionals to take our symptoms seriously, let's extend the courtesy to patients with other illnesses.