Insomnia (2.5e Flaw)
From D&D Wiki
If you have Insomnia, then your character has the inability to get any (restful) sleep. This may be an effect of something simple like herbal remedy, excessive drinking, exhaustion, or a lasting effect from a magical pall- among other severe injuries.
Insomnia may be contracted by those that are unused to a nomadic lifestyle moving to different climes, but may simply be from being forced into uncomfortable or unfamiliar situations.
This effect has differing levels of severity, some of which include general grogginess during waking hours or irritability, but more advanced types may be as severe as bouts of memory loss, inability to remain conscious, and other motor failures.
Less severe cases inflict -1 or -2 to certain rolls (for dexterity, strength, speed, and typical use of arcane) while the most severe cases can inflict dehydration, severe debuffs on will checks and Charisma rolls- Provided they don't overwhelm the character and render them unconscious first.
Takes double the time to cast conjuring spells.
Your character is functioning on a dwindling amount of sleep. They will- obviously- be overly short tempered ( even more so than usual in the case of grumpier characters).
Happy/Chatty characters may become somber, and quiet as they battle against unrest. Lively/Determined characters may become depressive or passive, while others may become arrogant as their rest yields them less and less recovery and they fear their efficiency slipping from them.
Insomnia is taxing, much in the way poisons are. To play your character around insomnia, you need to take into consideration the severity of it. Losing a night of sleep isn't going to immediately ruin the Cleric's faith, but months of bone-splitting wear on him might just.
Your character must require sleep to be afflicted with insomnia.