For me it is very hard to tell how my mental health is. I usually track it by looking back at conversations with people I care about, which can get weird. When things get bad, I tend to dissociate a little as a sort of defense mechanism. This time last year, I was more of an automatic process than a person, which was caused by essentially being the only person responsible for maintaining undocumented legacy software with a very critical manager who had never managed a developer before and didn't understand the requests he was making. This combined with an expensive chronic medical condition and the inability to save enough money to support myself if he finally fired me caused me to basically check out.
Now things have completely flipped, and it's pretty confusing. I got a job that I like and switched industries from healthcare infrastructure to manufacturing, and I actually believe in my company / like my manager / make a little more money, and by living in a house with 4 friends I've known forever I'm saving a ton. But I also have a 2.5 hour round-trip commute, and live in a city with such bad infrastructure that things like getting groceries have a huge amount of friction associated with them.
The weird thing is that the tiredness/lack of spare time/time dilation that comes with a living situation like this feels like dissociation, and the fact that I can't move forward with my previous goals effectively makes me feel like I am atrophying as a person. I'll probably do this for another year or so.