It's always drowsing and will never wake up. It can attack without waking up.
It acts as if it is affected by the Sleep status condition. All special effects of moves based on the Sleep status condition affect this Pokémon such as Snore & Sleep Talk working from the Pokémon with Comatose and double damage from Hex & Wake-up Slap, Dream Eater & Nightmare and even abilities such as Bad Dreams will activate. This Pokémon can still attack.