hi there, my thirteen yr old dog all of the sudden has become a different dog , literally over night. he has never had any health issues and still at 13 has tons of energy, walks at the dog park everyday and still want to play. this morning i noticed he was moving very slow, and is lethargic, he is not himself. he wont eat, and has his his down, his heart is racing and im freaking out...i know he old but why did this hapoen so fast?