He's having a toxic reaction to something, if it couldn't be anything else than I'd suspect the flea drops, what ever it is he's in a bad way and you need to get him to emergency.
My Dog Has Been Pacing For The Last Few Hours. He Is Drooling Real Bad. And Just Cant Be Still. I Wonder If He Is Having A Reaction To Flea Drops I Put On Him Last Night?
I don't think flea drops would cause such a reaction. Speak with your vet, there might be another ailment with your pet. Hope it all works out.