My Dog Is Acting Weird. He Is Following Me Around

My dog is acting weird. He is following me around smelling me like he doesn't know who I am. He keeps licking me and his whole expression is "different." He even went up to my son in law "sniffing" him and trying to be friends. The last time he saw my son in law he was barking non-stop. He doesn't normally follow me around sniffing and licking me, or anyone else. Since this afternoon, he has four different people and that's not like him.