I train a lot every week and sometimes after a very intensive training, when I hold my breath, I start to become dizzy. I did that about 3 times in the past, and the last time I did it I completely passed out.
It was quite scarry, mainly because I never passed out before. Is this an extreme case of something like thumb-tripping enhanced by the intensive training? Or is there something wrong with me?
Needless to say, I haven't repeated it since then...
(Also, I become dizzy after 10 seconds, but in normal conditions I can hold my breath over 2 minutes...)