I think you have touched on another aspect too there Hoobley.
From my personal experience many people experience one form of astral travel/projection at some stage in their lives, most not knowing what it actually is or dismissing it for dreams, etc. But I think its highly possible that many people with mental disorders or problems are not aware of what they are doing, nor ho to do it safely, or properly, or simply prevent themselves from doing it full stop.
Part of the major teachings of most pagan relgions is the understanding and correct use of AP, and how to stay safe doing it. It is not something that should be taken ightly as it can lead to things we are not prepared for.
And I think that often these negative aspects and contacts could manifest as something most classify as a mental disorder or disease.