I usually made some effort to appear together, but nothing fancy or too revealing. A bit of eye makeup. Always clean but it can be any outfit I am in the mood for (and/or appropriate for the day's other activities) and sometime pre-planned - from very causal to formal. I do these things for most professional meetings except with colleagues I see everyday, including doctor visits, so therapy was nothing special in this regard. I would never wear PJs outside of my home.

Typically, when I felt so bad that I did not have the energy and ability to clean and dress up properly (exclusively related to drinking episodes in my case), I rather just canceled than showing up as a mess. Maybe not the best for therapy as I was often clearly hiding my biggest problem. When I "only" have some depressed or anxious mood but sober, I can usually still get together properly as those moods alone are never too severe for me. In those cases, it usually helps quite a bit to make the effort to get clean and wear decent clothes, it can help me change the mood quite a bit, and I did that in therapy as well as just in everyday life. So self-neglect and sloppiness, for me, was quite intimately associated with alcoholism, nothing else really.

My second T once commented that I dressed in interesting ways and had obviously very good self-care - I clearly managed to fool him in a sense that he only saw a fraction of the truth. So I do believe that whatever someone is wearing, their grooming etc can reflect their mental health, but not in the same way for everyone. Some people are just naturally not interested in their appearance and clothing and can still have very good mental health.