I'm sure it depends alot on the child. Christopher has had a few cases of bad vomiting. If it is more than an hour after his medicine we'll try and give a stress dose, but not worry if it comes back up. We haven't needed to inject him ever yet. The most worrying thing is low blood sugar, and sometimes flat lemonade is a good thing to give as fluid to get the sugar down. We don't tend to stress dose for diarrhea and he's managed to get through some bad bouts of that! Basically don't panic. Things are usually not as bad as they seem.