If you already are asleep another status affect can not be used. If you are asleep then the Toxic orb will not be activated until you wake up, which will poison you at the end of that turn (If you survive).
Source: Bulbapedia
'Non-volatile status conditions, officially called status problems, are status conditions that will remain until a Pokémon is healed at a Pokémon Center, a specific curative item is used, or, in case of freeze and sleep, after a certain number of turns during the battle. A Pokémon inflicted with a non-volatile status will still be affected after being pulled out of battle (unless they have the Natural Cure Ability), and after a battle is over. It is only possible for a Pokémon to be afflicted by one of these at a time. In Generation III and beyond, certain Abilities will cause or prevent them, as well as benefit from them.'
