There are huge battles over the DSM about just how sophisticated those diagnostic tools are and the fact that psychiatry still struggles to achieve the evidential basis that the rest of medicine is expected to achieve (even if it too, often, fails in practice). Not many would argue that homosexuality is a mental disorder these days, but it was once. Other elements have been widely discredited (the movie industry still salutes them for multiple personality disorder though). It's shifting and subjective, and in many parts, defined by western cultural expectations (and hence, overbearingly American).
Medicine, of course, is often about drawing lines. Many medical organizations publish extensive reams of guidelines. Think of cholesterol, levels of PSA, etc. Where we set those lines defines how many people are 'ill' and the volume of treatment. Pharmaceutical companies aren't shy about lobbying for changes or getting patients and their family to do it for them. A small change can be worth billions. But anyway, we have to draw those lines based on what we know, and maybe in some cases lines shouldn't be drawn, since every line is an arbitrary border.
If something is rising in a population, then there needs to be cause. We can assume that something exists at an innate level in that population and diagnosis is essentially 'catching up.' Though if we suppose something to be a sustained level in the population, then it must be genetic or cultural. In a related paradigm, there's diagnostic creep, in which we expand categories and essentially move those lines. It's not necessarily a negative, we may previously have been ignoring genuine problems.
Beyond that, there must be a cause. An aetiological agent. Covid levels climb because there's an infectious virus. It doesn't have to be a physical agent, of course, it can be cultural. There is no shortage of examples. No one likes this one though, the medical paradigm we have is that diseases need to be caused by actual things and actual things can be bopped on the head with a pill. That's why, when we've worked up the vim to go visit the doctor, we feel curiously bereft when we don't leave clutching a prescription (even though 'there's nothing wrong with you' ought to be a relief). It creates a curious dissonance between patient and doctor. We wouldn't have booked the appointment if we were fine, after all.
I think the paradigm we have for western medicine only works to a point (and perhaps we should learn from other cultures). I forget the actual proportions, but around 80% of GP appointments are taken up by 20% of their list, and the majority of those have nothing demonstrable wrong. A fair number of those will be subjected to tests and procedures which are both expensive and likely unnecessary. So maybe there are better ways than chasing a diagnosis or reaching for pills. Often prescribed treatments are poorly evidenced and little more than a dangerous form of homoeopathy. We risk committing people to a lifetime of medication (that may be ineffective, and regardless we don't know the long-term implications of) and defined ill-health. It's not necessarily even cheaper than the alternatives.
Before the usual and inevitable pile-on by the group's righteously frothy fringe, I think these things are real. Not everything needs an organic cause. If I say I feel tired right now, it's because I feel tired. It doesn't matter if I had a good night's sleep. But the solution to my feeling tired might not be a sleeping pill.
The funding of healthcare is finite and in the (I was going to write mid) short-term is not sustainable. Something has to give and we have to give serious thought to a simple 'medicate more people' method and also the lack of investment in sustainable and healthy lifestyles. The practice of medicine must stop being reactive and become proactive.
(The statistics in DSM isn't a reference to methodology, it's a call back to its origins as a military census.)
