Sure, but that is a bit of a tautology. If something is a "mental illness" then it is something that happens to the person beyond their control/choice. But it isn't clear that most of what the OP is referring to qualifies as a mental illness, and could be forms of self-reinforced negative affect that is under people's control, or at least are learned patterns of responding that they could control.
Basically, clinically diagnosed chronic depression can be a mental illness, but self-reporting the symptoms that qualify as having had an MDE is not a reliable index that one has such a mental illness.
ron,
I'm back on firm ground.
IMHO medical professionals are not fools, and they will know what they are looking at. Whilst they will take serious account of any and all of a sufferer's self reporting, there are many other markers in body language, behaviour and attitude that are quite obvious when you've seen enough of it.
I worked with mental health sufferers for several years, as part of my teaching job with adults. I don't remember a case of a person referred to the courses in error. Towards the end of the job, I could tell an ill person just by seeing them walk in the door and sit down. A depressed, anxious, obsessive, bulimic or anorexic person was ill in plain sight in front of me. I'm sure that psych docs have developed much better skills.
Also, I'm still working as a mod and helper on a mental health support forum. In that media there are only written words to go on. It is remarkable how similar the patterns of reporting are, and how clear it is what is dominant in the posters thinking. Another thing that's happened is meeting posters in 3d, if they happen to live near enough and want to come to a relaxation class. On such few occasions I have been saddened by how unwell those people were, despite having kept up a better impression online. I think this is a very common phenomenon.
Finally, the real danger is failing to take reports seriously enough. I have personally known two young people who committed suicide, both under the age of 25. Once that has happened it is too late.
Alex.