Sleep

 is a derived statistic in Fallout: New Vegas in Hardcore Mode.

Characteristics
Sleep is a measurement of the raw time you've spent awake. Beverages containing a bit of caffeine will help keep you awake longer, as will stopping your adventure and taking a nap. Not sleeping for two weeks will cause you to die.

Bugs

 * Sometimes the SLP gauge in your Pip-Boy can get stuck on zero, and in fact will not display any number below the indication arrow. During this time your character will not advance in sleep deprivation. This bug may be fixed by finding a bed and sleeping for any amount of time. After the player wakes, the gauge will begin displaying a number again and will increase over time normally.