Armchair diagnosis is dangerous IMO. It can be a form of gaslighting. Sure everyone can benefit from therapy, meditation and improving systems for managing sadness, frustration, impatience but telling yourself or someone else you have ADD, compulsive disorder, anxiety is a great way to pop the self esteem bubble and confidence you need to get through life.

In the workplace it's especial dangerous; you can force someone to question why they don't like a job or feel isolated or bullied by convincing them their perception is really the problem.

It doesn't take much effort to convince someone who is upset by circumstance that they have a problem. "You're too sensitive" "you're depressed" "that person has an anxiety problem" when really the environment at the job might really be the problem or some basic coaching might be the solution.

I worked somewhere in which people openly admitted the company culture drove them to therapy yet were so "grateful" for an "open and inclusive" environment. The cognitive dissonance there was very disturbing.

This occurs in families as well. I grew up in an abusive household and, well damn, your parents will do their best to convince you that you are the crazy one and need help.

When I was a teen I ended up in a lot of outpatient mental health stuff (similar story, abusive parents who were very convinced they were normal) and the girls I was friends with there would outcast anyone who started diagnosing people colloquially like that from the main group. If anyone does it to anyone in my life I instantly write them off as a moron and probable manipulator.

How do you, as an individual, tell if it's you or if it's the environment?

I wish I had a good answer. A mix of trusted friends and a thoughtful therapist. If you are in an abusive situation, a therapist should be able to identify it since there are objective frameworks to think about that. It's also easy to reject an "objective" diagnosis of a situation because you are likely to view it from your internalized perspective.

A strong hint is if you change the environment, and the problems suddenly disappear.

If the problems disappear slowly, it could have been the environment, but it also could be your personal growth. But if they disappear overnight...

You speak with a professional

Disorders are classified by more than just one or two observations. The problem is people thinking that normal reactions to life is are the result of a disorder.

Case in point, there's a range of responses to trauma. Having bad memories or occasional nightmares as a response to trauma is normal. PTSD is not normal. Less than half of people involved in severe traumas will have problems coping normally and fewer develop diagnosable PTSD.