I think Nick Sands explains it profoundly in his brilliant article "Just a wee bit more about DMT"
"DMT is the weaver. Whatever you give DMT, it weaves this into patterns. If you are a doctor sitting in a hospital room filled with people watching a “subject” and injecting said subject with DMT while people are acting out their roles of nurse, doctor, researcher, government representative, etc., and your subjects have little alien robots, insects, reptiles or what have you, crawling all over them, probing and examining, is this really so strange? You are just seeing a DMT woven projection of the very environment you have created. What would happen if you changed the environment?
Suppose now, that instead of a hospital room with beepers and weird electromagnetic currents in the subliminal environment and medical personnel with odd motivations and curiosities, you were in a beautiful wooden house in the woods with a stream outside making gurgling and tinkling sounds. Inside there are friends in casual clothing—soft, tastefully-colored robes. Men and women dressed for a celebration, seated on velvet cushions on oriental carpets with candles and flowers, and beautiful music. Flowers in vases, mandalas, and wondrous paintings on the walls, aesthetically lit by natural and traditional lights, not fluorescents. A fire glowing in the hearth, multicolored fish swimming in an aquarium. Before you is a teacher who has decades of personal DMT experiences who is serving as your travel facilitator. You’ve prepared for days with yoga, meditation, and pure food. What kinds of trips do you think happen in this type of environment?
Instead of reptiles, aliens, and robot doctors, you have Gods, magicians, celestial and magical beings—intimating, winking, indicating, and even speaking to your inner being with lessons of love, healing, inspiration, and creation. You enter into the temple of the source of creation. Everything is ensconced with magical, crystalline beauty. Your heart and mind fuse in loving understanding that heals the rifts in your heart. Tears of gratitude stream down your face, joy lights in your being. Everyone around you understands your bliss— you don’t need a support group of fellow “subjects,” so that you won’t think that you are losing your mind."