"It's so cute when it's sleeping, isn't it? Actually, it's still as abhorrent as ever, but at least it's not trying to kill us."
—Noyan Dar, Tazeem lullmage

Narcolepsy

Enchant creature
At the beginning of each upkeep, if enchanted creature is untapped, tap it.

The List

Jumpstart

Modern Masters 2015

Rise of the Eldrazi

Narcolepsy doesn’t keep the enchanted creature continually tapped. The creature untaps during its controller’s untap step as normal, then is tapped when Narcolepsy’s ability resolves during that upkeep. The creature may be tapped in response (for example, if it has an activated ability with {T} in its cost).

Narcolepsy’s triggered ability has an “intervening ‘if’ clause.” That means (1) the ability triggers only if the enchanted creature is untapped as any player’s upkeep begins, and (2) the ability does nothing if the enchanted creature is already tapped by the time it resolves.