It's hard to say just with the info given.
Is he up to date on all of his shots?...especially Parvo.
Are you feeding him a quality dog food that doesn't have alot of fillers?
Have you changed his diet recently, or given him table scraps?
Do you take him out for daily exercise?
Could there have been something else he got a hold of while eating leaves, or were the leaves wet and rotten? (that could upset his little tummy)
Your best bet is to take him into the Vet on Monday just to be safe if you are noticing he's not himself. Better safe than sorry right?
Hope your little guy is fine, and maybe he just likes hanging out on your lap.
