My first memory of that experience was a cacophony of noises, specific images, and what I can only describe as colored static. Then, over what subjectively felt like 10 seconds, I realized at some stage that I was ‘awake’ and the various sounds and images sort of faded until I had one coherent thought and then started to get awareness of my surroundings and then finally opened my eyes.
It was a very unsettling, but also very interesting experience and sort of made me curious to investigate if this is what people experience with hallucinagens.
Another time when I had to make a trip to the ER they gave me nitrous oxide when they tried to reset a broken bone and I had very interesting aural hallucination where sounds became chopped up/echoey. When the gas stopped I asked the nurse how long it had been and she said about 5 minutes but it had felt like 30 mins.
Both of experiences left me fascinated how malleable our perceptions are :)