My experience happened around 1990 or 1991 in New York City.
I attended an all-day Saturday spiritual/theater/dance/workshop. Through out the day we did many types of activities and exercises, most of which included meditation, movement, voice and acting exercises.
When I left the workshop, I was definitely in an altered state of consciousness: feeling very light and like I was walking on clouds. It was around 4:30 pm or so and I decided to stop, on my way home, at the (what was then) the Red Apple Market on 13th ST. And 7th Avenue, to get something to eat or to buy something to take home. It was a very small grocery store and very quiet at this particular time. I took a cart and noticed the two cashiers in the front, and then began slowly roaming the 1st aisle. I was about halfway down the aisle and was staring at the mayonnaise contemplating making some tuna salad, when all of a sudden there was a very loud exhale of breath right in my right ear. I could hear and feel the breath. It was chilling to say the least. I immediately turned my head quickly around and saw a man standing about three feet away from me. He was very scraggly looking, about 75 years old with long salt and pepper hair, with very piercing blue eyes and heavy eyebrows. He just kept staring at me and didn't say anything. He seemed angry and seemed as if he was looking through me. I thought he was some crazy homeless guy that must have wandered in from the street and was just trying to scare me (a common occurrence when one lives in Manhattan). He was successful at that, yet I immediately told him firmly (something I won't repeat here) to get away from me and leave me alone.
I quickly took my cart around the corner to the next aisle but then decided I should tell the manager in the front what had happened, so he wouldn't bother anyone else. I went directly to the front of the store and repeated my story and asked if they could tell the man to leave the store. The manager and the cashier both looked at each other then looked at me like I was the crazy one and said. "I'm sorry but you are the only person in the store and have been since you walked in." I said "No, no you must have missed him. He was right here in that 1st aisle." They both just stared at me. The truth is they were at the very front of the store. The store had turnstiles and I think they probably would have seen someone else come in, but at the time I left thinking they must have missed the guy.
It has stayed with me ever since and it wasn't until many years later that I realized the man had to have been a full body apparition, made possible by my altered state. I believe I was only able to see him, at that moment, because of it. It is the only explanation for what happened that day at the Red Apple.