Thank you for the additional information.
Eating grassing and heaving indicates nausea. What can cause nausea well,
*eating a different food,
* eating something they should not that causes a blockage in the digestive tract
* Eating something toxic
* Intestinal parasites
* Bacterial infection in the digestive tract.
* Problems with the liver or kidneys
These are the most common causes but not meant to be a complete list
If he is acting normal other then the heaving you can try to treat this at home. Pepcid AC at a dose of 10mgs per 40lbs of body weight every 12 hours.This will help with the nausea
I would offer a bland diet today of boiled chicken and rice in small meals.If he refuses the bland diet, continues to heave or vomits, is not passing stool is having diarrhea or declines in any way I would get him in to see the vet today for some tests since we are unsure if he may have gotten into something toxic
I hope he does ok, and this is just a little stomach upset. Please reply back if you have additional questions or concerns