Sweet Veil prevents the Pokémon with this Ability and its allies (including non-adjacent allies) from falling asleep. Rest will fail when used by the Pokémon with this Ability or an ally (unless the user has an Ability that ignores other Abilities).
Sweet Veil causes Yawn to fail if used on the Pokémon or its allies (including non-adjacent allies), and prevents the Pokémon and its allies already drowsy due to Yawn from falling asleep.