Well Rested

A status effect that grants the player a +10% experience boost for 12 hours after sleeping.

The  effect is obtained by sleeping in a bed you own (i.e. in your Megaton house, your Tenpenny Suite, or a rented bed) or a Queen Sized bed that can be found in the ruins of buildings, like Alexandria Arms. The effect lasts for twelve hours from the time you awake, regardless of how long you sleep. If you sleep in any bed it will cancel the effect but if it is a Queen Sized bed or an owned bed it will return immediatly.