For my story, I had to do a lot of research on mental health because my main character deals with panic attacks and depression.
So I'm looking into trigger warnings, symptoms of after having depression or panic attacks and to know what's the difference between an anxiety attack and a panic attack because they are both different. Then to know body reactions after having episodes and also treatments to deal with episodes like breathing exercises and counting or doing the 5 senses (touch, smell, sound, etc)
Then I did a bit of research for medicine. PTSD as well. High function Anxiety Disorder... Signs when off medication and body reaction as well because of relapses.
It's just a lot to make sure you know what your writing when it comes to mental health