During deep meditation, experienced meditators frequently report spontaneous visual vision in the form of lights or other forms of visual imagery. These encounters with light are commonly understood as having mystical significance.... Meditation can also lead to hearing sounds without external stimulation, feeling sensations without physical causes, and seeing images that do not correspond to anything in reality. These experiences are not uncommon among practitioners who have reached a certain level of meditation proficiency. They are indicators that your mind is working sufficiently below the surface of awareness where real-life problems don't interfere. If you're interested in exploring this subject further, I recommend these books: Mystical Experience: A Study in Religion by Alfred Liefrinan (University of Chicago Press). This is a classic study of mystical experience as it has been recorded over many centuries by many different cultures around the world. It's a great place to start because it's short and accessible, and will give you a solid foundation to build upon. Visionary Consciousness: An Introduction to Humanistic Psychotherapy by Robert Moss (Jason Aronson). This is a recent book that explores the relationship between consciousness and health, taking a cognitive-behavioral approach to treating psychological disorders. It's helpful for anyone wanting to understand how visionary experiences can be used therapeutically.