A problem with modern psychology is the diagnostic criteria aren't very much based on underlying causes as on being able to reliably diagnose patients based on symptoms regardless of physician. This leads to people agreeing what your diagnosis is without a strong or particularly useful set of understanding of what caused it or a specific treatment to change those causes (which is why so many people are on SSRIs). Historically there just wasn't much to go on when it came to determining underlying causes but neuroscience is catching up with understanding much more about how brains actually work.
The point is "depression" or "PTSD" probably don't exist among many others. There are perhaps dozens or hundreds of unique conditions currently lumped together because they present in vaguely similar ways - the good news is that we are making progress towards much more arguably "real" understandings, the bad news is we're still quite far away from diagnosing mental conditions with the same specificity we can diagnose cancers or viruses.
The point is "depression" or "PTSD" probably don't exist among many others. There are perhaps dozens or hundreds of unique conditions currently lumped together because they present in vaguely similar ways - the good news is that we are making progress towards much more arguably "real" understandings, the bad news is we're still quite far away from diagnosing mental conditions with the same specificity we can diagnose cancers or viruses.