Hello children. It has been the obligatory 657 years since I wrote my last pointless blog. Time for a new one! But this one has a purpose. (Also by the way this contains some spoilers for two books called Cryer's Cross and Bone Gap incase you may read them. I don't recommend Cryer's Cross though)

If you're going to write a story, don't give your characters disorders just for the sake of giving them disorders. Have a reason for it, basically follow Chekhovs gun. If its in the story, it needs to be used meaningfully later AND IT NEEDS TO BE RELEVANT! Don't give Mary Su PTSD just because you can and have a reason for her to have said disorder.
I have read two books this year that have characters with disorders just for the sake of having them, and let me tell you it distracts from the story a lot. Especially if you don't understand the disorder you're giving the character.
The first book I read that has this problem is called Cryer's Cross. It follows the story of Kendall who has OCD, her life is going fine until suddenly her best friend goes missing and whenever she sits at his desk she hears voices talking to her. She has no reason to have this disorder. It adds nothing to the story except the ending where it "saves" her even though in reality it had nothing to do with anything. The only real reason she has OCD is "gotta make it relatable somehow lols" if you took out that fact it would change NOTHING in this story. If you're curious by the way, the way her OCD "saves her" is once she's buried herself underground she suddenly realizes "wait lol wtf am I doing" ah yes OCD totally caused that. Apparently OCD breaks ghost hypnosis or something woo hoo! But see, she really had no reason to have OCD it didn't add anything it was just given to her for the sake of giving it to her. Besides the only compulsive behavior she has is straightening up her school room, I don't think that'd snap her out of the ghosts telling her how to "save" her best friend since this happened at night.
The second book was called Bone Gap. The book follows our main character Finn who lives with his brother in a small Midwestern town. The book starts after their friend Rosa is kidnapped and Finn was the only one who saw it. Too bad no one believed him because he couldn't describe the mans face. Why couldn't he? Oh well he was face blind of course!
You don't even learn this until like the last few chapters! It adds NOTHING either. Seriously it could've had a perfectly normal reason as to why he didn't remember the kidnappers face or maybe his face could've been covered. But nope! Face Blindness.

I am in no way trying to tell you that you can't or shouldn't give your characters disorders. Its your story, but if you do research what it is and how it works, have a reason for giving your character said disorder and have if benefit or even set the story back. As long as it makes sense and isn't just because "o I want to" and if you're going to use a disorder like depression or something serious do it tastefully.