> but it seems in these cases, there is a very fuzzy boundary between the symptoms of depression and "the real illness": brain fog, lack of energy etc.

It is possible for someone with depression to misdiagnose themself with Long COVID or CFS if they don’t understand the conditions. A lot of people will avoid mental health diagnoses in favor of other explanations because they don’t want to accept that they have a mental health condition.

Where you’re confused is that these conditions are not exclusively defined by “brain fog” and lack of energy.

CFS has specific criteria such as specific post-exertional malaise that set it apart from depression in a very concrete way. Any informed practitioner or screener for study acceptance is going to identify the difference.

Onset also matters. If someone claims they developed Long COVID and the trigger was a bad breakup with no known case of COVID it’s easy to dismiss. A key feature of Long COVID is that it starts with a case of COVID.

As for your posts: The fact that you included Morgellon’s (a fictitious disease akin to delusional parasitosis) with other real conditions suggests that you are picking up some weird information from somewhere. Please don’t speak so confidently about these topics you don’t understand. Curiosity is good, but dismissing other people’s conditions as mental illness is really awful.