Paul was very much in the side of his own experience. In Galatians he said, It pleased God to reveal His Son in me. In 2 Corinthians he wrote, God who said 'Let light shine out of darkness,' has shined into our hearts to give the light of the knowledge of the glory of God the face of Jesus Christ. Paul had numerous extraordinary spiritual revelations and experiences. He did not sit down and reason out a consistent and cohesive theology, rather he "received" a series of insights. He believed his experiences so much that he argued with James the brother of Jesus and Peter the apostle. He followed his own experiences and set The Way on a different path than the one that would have developed if James and Peter would have won.
Most of Christian theology relies heavily on Paul's writings. Creeds and codes came along, written by men without such experiences who tried to interpret (without the ability to know directly) what Paul meant or tried to frame it to control others for profit or power. Think Council of Nicea for example where a small minority of bishops worked with Constantine to unify his empire by standardizing acceptable beliefs. Don't get me started on this and countless other good old boy conflabes that twisted Jesus' teachings into unrecognizable distorted shapes.
On the other hand, less than mentally healthy men have had delusions and hallucinations that led people in ugly, hideous ways. Think Jim Jones or David Koresh in the 20th century, for example.
So how do we discern the difference between genuine divine experiences and mental illness, either our own or those of others?
For me, it is an evolving hybrid. I read and reread, and have done so since childhood, the words reputed to have been from Jesus or at least paraphrased by the late first century writers of the Gospels. I study great thinkers in a wide spectrum from Marcus Borg to Meister Eckhart, from Bart Erhman to Hildegard of Bingen, from Richard Rohr to Thomas a Kempis, from Aldous Huxley to Augustine. I have read the thoughts of hundreds, maybe thousands, of thinkers on Christianity and on other religions too. It is my passion to quest for knowing, and has been for as long as I can recall. It really calls to me.
And, since childhood, I have had numerous experiences of the Divine. So, I measure my spiritual experiences with the words of great thinkers, thinkers also on a quest. I run from the self-satisfied know it alls. The Infinite cannot be totally known, hence Infinite. It is an ongoing journey of awakening with twists and turns for sure, but it can only be walked by the sincere, the open, the humble, the genuine seeker.
I hope and pray that you too are on such a quest. This weary world needs you.