From your description it sounds like your fella had a vasovagal response. This can occur in people as well during vomiting episodes. Essentially, the vagus nerve is stimulated to the point of significantly but temporarily dropping the blood pressure and heart rate and the result is fainting.
Most of the time it is a one time event however it isn't uncommon to see this more frequently in animals with underlying heart problems. As long as he recovers uneventfully from his vomiting fits then I would be sure to bring up this episode with your vet the next time you see him.
If he continues to have issues with vomiting or in a day or so seems to have respiratory issues like an increased respiratory rate or effort then I would be sure to follow up with your vet.
Causes for vomiting can be many. In younger dogs my concern would be foreign body ingestion/toy, bone, rawhide, etc. Intestinal parasites are also a concern. Lastly, viruses can cause vomiting.
Let me know if I can assist you further and how he is doing.
Thank you. Does it matter that he doesn't seem to be hungry? He's up and about but his food has been untouched since lunch time yesterday.
That is concerning and I suspect he is nauseated. I would also want to be sure he is evaluated for any aspiration pneumonia that might have occurred after the vomiting. Try mixing canned dog food in with his dry or mixing some chicken in it to see if he eats. If he continues to vomit after eating then a trip to the vet is warranted.
Thank you! We waited it out and he started eating on his own. He's good now.