Only once, all the other times were just blackness. That one time is one I'll never forget, though.
Back in the '90s, I knew a girl who was interested in helping me CTB by standing on my neck until it was done (I offered her the option to take whatever she wanted from my house once it was over). I hadn't refined my methods or identified that I never wanted to be found back then, and I sure didn't think (or care) about what would happen for her afterward... I've grown a lot since then.
Anyway, she stood on my neck with her foot wrapped around and pressing on the arteries a lot like suspension... and I blacked out after a few seconds. My memory of the time I was out was of being a bird--like a dove or maybe a pigeon--flying really high. It was nighttime, and I was above a really large city with lots of big, lit up buildings, maybe New York City, though I couldn't be really sure. I had a vague sense that I had had a life before, but couldn't remember anything about it and it was little more than a small thought in the back of my head. I remember soaring on the air and thermals, not really caring about much, just soaring because that's what was in my nature. I did a few loops, then sailed for what felt like maybe 30-60 minutes. Then something happened, and I was falling... I can very (very) vividly remember passing between the tops of the buildings, seeing the windows of the buildings go by as I fell (some with lights on, most of them dark), seeing the street approaching and even seeing traffic on the street not really noticing me. Just as I hit the asphalt, I woke up disoriented.
The girl who had been standing on my neck was standing in the corner just staring at me. She said she had stayed on me while I was jerking and convulsing, and that she didn't get off until I had been completely still for a little while and she thought it was done. She said I had been out for about 10 minutes. If all of that is true, I have no idea how I survived, but here I am.