Dogs will eat grass when they have a upset stomach. The grass helps them to vomit and thus release the Nashua feeling. The bad news is this is not good for your dog. Grass can cause many problems such as blockages.
The main issue is curing the underlying problem of the upset stomach. In the mean time you will need to keep a close eye on him to prevent him from eating more grass.
If he becomes lethargic or you notice blood in the stool or vomit, he needs to see his vet promptly. As this is a sign of serious illness including a parasite infection or a blockage among other things. This sounds like a case of upset stomach. You can self treat this at home unless any of the above symptoms start presenting.I would start him on a bland diet of boiled chicken and rice to help settle his stomach. I am concerned with him becoming dehydrated as this is quite serious with dogs. I recommend giving him unflavored pedilayte to replace the electrolytes he is losing with the vomiting. You can also give him One teaspoon of Pepto Bismol per 10 pounds of body weight for faster relief.I hope he is feeling better soon, Please let me know how he is doing.Walter
Upset stomach can come and go with dogs, it may or may not have any other symptoms so this is not a concern that he is acting well. The fact that he has a good deal of energy is great........the last thing we want though is for him to start losing that energy so we need to curb the grass issue and settle his stomach down.
Pedilayte is a drink designed for children to prevent dehydration. It has electrolytes that normal water does not have. When a dog is vomiting, the water is purged faster and thus the dog is not able to hydrate fast enough. The pedilayte to designed to hydrate faster then water which will prevent him from getting dehydrated. You can find Pedilayte at your local grocery store. If you like you may mix it half with water 2-3 times a day as long as he is not experiencing any signs of dehydration. Once the vomiting stops completely you can resume water only.
The bland diet will help settle his stomach so he will not feel the need to eat the grass. As long as he is eating the grass he will continue to vomit so you must curb that immediately.