Due to being sick with mono and dehydration, I passed out after a long time being in bed. I was unconscious for thirty seconds, and was held upright, so my brain couldn't get any oxygen. I was unconscious, so I don't know if I was breathing or not, but when I woke up I was told I was very pale, almost grey, and my lips had a blue tinge. This went away quickly after recovery and my skin colour was back to normal.

Is this any cause for concern? All the tests run on me came back normal and it hasn't happened again.