I never had an alien encounter on acid, but I did have a transcendental experience once. I was tripping and doing whippets with a couple of friends. It was some really clean acid straight from a Grateful Dead show and I did two hits. We were taking turns doing the whippets with a balloon and on one of my turns I decided I wanted to try doing two cartridges at once. I had something like a near-death experience with fog and a light, and came in contact with what/who I somehow knew was God. He offered me the chance to go with him right then and there and be at peace with no pain, or I could go back to life and my life would be difficult, but I would be able to help a lot of people. I chose to go back to my body and immediately came to with my friends standing over me slapping my face and asking if I was okay. They said my lips were turning blue and they were scared. It was quite an experience. No aliens though.