Hello and thank you for asking your question on just answer. My name isXXXXX will try to help.
It sounds like he has an upset stomach.
Is he vomiting or having diarrhea?
Is he retching or having dry heaves?
How much does he weigh?
Ok lets try this:
Do not let him eat anymore grass, or have any food or water, right now.
You can give him 1/2 of a pepcid ac tablet to reduce the acid levels in his stomach.
You can also give him a teaspoon of pepto bismal.
That should settle his stomach.
Do not let him have anything else by mouth until he is feeling better.