Also, when using the bag, remember that when you breathe back in, take the bag away from your mouth, otherwise you will ingest what you just used you entire body to expel.... ask me how I know this...! (It wasn't me, but I could hear the guy in the back seat...).
Another piece of advice is that once you start to feel ill, you are unlikely to start feeling better until you are on the ground, ie it rarely seems to get better by simply toning it down.