Did he eat something that he should not have? Any chemicals on grass that he walked on? That would make me more concerned. Drool could be a prelude to trying to vomit.
However it could also be related to completely normal teething in which case I wouldn’t be concerned
When you say his energy was good does that mean he was behaving completely normal or was he a little hyper. If he was a little hyper, that too would make me concerned. Normal behavior, not so concerned. Lethargic and sleepy when he normally wouldn’t be is also concerning.
Was he eating normally, pee and poo typical? Then I’d be a little less worried.
Is it hot where you are? Whiskey drools when the weather gets hot. Even when he sleeps on a marble floor under the fan.
Then he drinks his cold water and makes his whole face wet, in addition to the panting and drooling..