I don't have any stats, but my impression is that about half of the questions asked here by new users are "what's wrong with me?" closely followed by "suggest me a treatment".
We obviously have a close reason linking to a FAQ for that, but I think it's perhaps better to have that link featured preventatively for new users. It would save them from typing long personal stories here. And it would save the regulars from the drudgery of closing a lot of questions of this type. (Of course the close reason needs to stay, since there's no guarantee that everyone will heed this proposed warning.)
I'm not sure exactly where this customized advice/warning could be displayed. If the "How to ask" (which is displayed to the right of the edit area) can be customized, that would probably a good place. There seems to be enough room there, assuming the box expands downwards if more text is added to it.
(I'll have to check how that box is displayed on phones though.)
I'm less sure what the message should say exactly. Perhaps something like:
Do not ask here for a diagnosis (e.g. "what's wrong with me?") or for treatment suggestions for your personal problems. Scientific questions about disorders, including their diagnosis and treatment, are welcome as long as they are asked in a sufficiently general way, so they are relevant for other users.
By all means, please suggest improvements to this in your answers.