Are mystical experiences delusional? How would you know?
To me, Phil, I try to never let this possibility get very far away from my thinking. For me, the day I decide my experience is definitely NOT delusion will be the day I have succumbed to delusion - in all senses of the word. That makes me a perennial "Doubting Thomas".
For the purposes of this thread, a mystical experience is an experience in which subject/object perception comes to an end while experiencing remains.
What amuses me so is that this quality, if you will, is just the tip of the iceberg to an entirely different way of perceiving reality. There is much more beyond this "feature", though as Ben D touched on, it is incredibly difficult to render what lays beyond this stage into words.
BONUS QUESTION: Is normal, non-mystical experiencing delusional? How would you know?
That's just it though, Phil. If it was a reality/delusion it isn't likely one would know. If everyone was in the same boat, their experience would simply mirror and support you own... gee... just like in "real" life.
Knowing (conceptually, at least) that you are in a
necessary reality/delusion does help though. Knowing that it is a self-created reality/delusion helps to allow one to poke out of that reality/delusion as perception permits.
Perhaps this is all confusing, but to me reality is something you never stop doubting. Delusion occurs when you remove all doubt.