Mental illnesses are not a topic to joke about. Still the topic is highly interesting for philosophers as well, since it poses the general question of "normal" human behavior, or how to deal with deviations from the norm. The ethical implications are therefore immense. When we talk about mental "disorders," is that already a political implication? Why would apparent order (health) be preferable to chaos in the first place?
In North America, the DSM-V is used for the diagnosis of mental disorders, while the European counterpart is the ICD-11. It is extremely informative to work out the differences between the two manuals. After all, this alone reveals that a disorder is based on a cultural background. Likewise, it can be generally observed that disorders are removed from the manuals, but also that new ones are added with each new edition, which is also an economic factor, insofar as statutory health insurers have to pay for the treatment of the affected patients - or not.
This is in no way meant to imply that the definitions in the works are arbitrary. There are several traits for each diagnosis, a certain number of which must be fulfilled in order to initiate the diagnosis in the first place. If you read through entries by way of example, you quickly get the idea that you yourself have fulfilled some of these traits, but you will still not receive a diagnosis from a specialist for a long time. The processes for this are extensive and usually also require several expert opinions. And there are certainly no diagnoses after just a few sessions.