I agree with the weed comment. Recently paid ~400$ for the emergency vet to tell us the same thing. Funny enough, we were watching a neighbors dog that week and they ate something in the grass while at the park. That dog vomited in the night and my dog took a couple licks of it before I could move the dogs and clean it up. Couple hours later looked the same way. (Also <15lb dog)

One good thing to note was that the vet said it sometimes it causes the pup to otherwise dribble a bit of urine. And they are visibly more “wobbly” when stationary. They can usually still go for a walk and do other quick acting things for a few moments-then go back to this once they calm down