St. Monica's feast day is today; her son's is tomorrow. Of the various mystical vouchsafings, glimpses, and intimations recorded by St. Augustine in his Confessions, the vision at Ostia (Book 9, Chapter 10) is unique in that it is a sort of mystical duet. Mother and son achieve the vision together. Peter Kreeft does a good job of unpacking the relevant passages.
Kreeft here lists fourteen features of mystical experience which comport well with my experience.
Related: Philosophy, Religion, Mysticism, and Wisdom