Source : Webster's Revised Unabridged Dictionary (1913)

Sleepless \Sleep"less\, a.
   1. Having no sleep; wakeful.

   2. Having no rest; perpetually agitated. ``Biscay's sleepless
      bay.'' --Byron. -- {Sleep"less*ly}, adv. --
      {Sleep"less*ness}, n.

Source : WordNet®

sleeplessness
     n : a temporary state in which you are unable (or unwilling) to
         sleep [syn: {wakefulness}] [ant: {sleepiness}]