Narcolepsy (3.5e Flaw)
From D&D Wiki
You have difficulty staying awake.
Effect: You take a -6 modifier to all saves vs sleeping effects. Once per day, the DM can choose to have you make a DC 5 saving throw with no modifiers. If you fail you fall asleep for 1d6 rounds. If you are immune to sleep effects, you are no longer immune.
Roleplaying Ideas: Sufferers of narcolepsy often have other sleep-related disorders such as insomnia, excessive daytime sleepiness and hypnagogic hallucinations.