I would have the vet check him for a tooth or peroidontal problem or something stuck in teeth or hard palate or gums etc today. Even a cut in the mouth can cause this or s string wrapped around the tongue.
Licking can also be a sign of anemia and dogs will lick and drool if they feel nauseaous even if they never throw up.
With a big dog one always worries about this being a pre bloat symptom. You can read about bloat here
www.marvistavet.com/html/body_bloat.html
But my suggestion is having the vet look at the dog today if you can possibly do that.
Hope this helps you!
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