I imagine, just like everything else, it doesn't work the same way for everyone. I have tried several techniques of this personally, including filling my lungs and holding my breath, and exhaling completely and holding my breath. The latter works better for me. I have no special training but I can hold my breath for about a minute if my lungs are full. The problem there seems to be that it gets me even sleepier. However, if I exhale and hold my breath it only takes about 10-20 seconds and the response is very immediate and sharp.

I should also note that I don't tend to pass out. Last time I came close to passing out, I was in a state where most people would have (blood pressure at 70/40). Perhaps this trick is not for you if you pass out easily.