This causes Rest to fail altogether. If a Pokémon is asleep and acquires this ability, it will immediately wake up; this includes when regaining a lost ability upon leaving battle. Yawn will fail if used against this Pokémon, and if it acquires this ability while drowsy it will not fall asleep.
This ability functions identically to Insomnia in battle.
If the lead Pokémon has this ability, higher-leveled Pokémon have their encounter rate increased.
Pokémon with Vital Spirit as a standard ability (1)