As always, your insights are spot on for me. I'm currently in the process of writing the third installment of my Hybrid Journey series and am tackling the main character's battle with depression.
I think there's a fine line between getting it 'right' so to speak, and it coming across as too much. What I mean by that is trying to portray the character's thought process realistically vs sensationally.
Every author has a unique vision of how they create their character, and developing a character who deals with insanity, no matter what form it takes, is a challenge.
I can remember reading a book about a character who gradually went insane. I can't remember the title or author but what stuck with me is the process of the character's mind as they slowly "lost it" over time. The author did a fantastic job of showing the readers what was going on in the person's head. Quite honestly, it was scary AF.