The only times it's happened to me were my first few times. Back then we smoked bad-quality hash (soapbar) mixed with tobacco.

Now I smoke (or smoked, I'm dry and without a supply these days ) the green weed pure with no problems. I can get royally shit-faced, and still feel great. I did notice some initial discomfort right after smoking a joint or from a pipe, but with a bong I've never felt anything like that.

But I'd still have to agree with earlier posters - just smoke until you feel content, then stop.

Happy smoking.