It is a good question you ask but there is a certain sector that might Blur the line between spiritual experience and a disorder.
Here is an ancient story of a real monk...
Once there was a monk in srilanka (about 2000 years ago) he used to practice "Attika Sanna". It is a form of meditation that focus on the bone structure of a being.He was on his way from "Anuradhapura" ancient city where he met with a beautiful woman. She was actually going to her parents place after a fight with her husband. She saw the monk and smiled. But the monk did not saw her as a person, He only saw her skeleton. Her husband was coming to take her back home but he was far behind. The monk went on his way and met the husband on the way, He asked "did you saw a woman going this way?". The monk replied "I didn't saw any woman but i saw a skeleton walking that way.".
It is good to take a look at what a disorder is...
Mental illness refers to a wide range of mental health conditions — disorders that affect your mood, thinking and behavior. Examples of mental illness include depression, anxiety disorders, schizophrenia, eating disorders and addictive behaviors. Many people have mental health concerns from time to time.
What science see as a disorder is something that is a bit far from what is normally accepted.But as Buddhists we try to change our mindset with meditation.It actually changes the brain structure.
Mindfulness Can Literally Change Your Brain
So a changed brain will not work like a normal one. It will most certainly behave in different set of rules.This would justify stories like the one above.
So how to recognize something gone wrong?
Buddhism's advice on that is to have a well experienced teacher who can understand and help. I must say that this person must be a Monk because a lot of times people who advice their friends on meditation get carried away by their ego and give misguided advice.