The Mayo Clinic explains the problem and the easy solution:
Extra zzzs may not cure those dark circles under your eyes. One common cause is nasal congestion. When your nose gets congested, veins that usually drain from your eyes into your nose become widened and darker. Rinsing your sinuses with a saltwater solution (mix 1/4 teaspoon sea salt with 2 cups warm water) or over-the-counter saline spray can help relieve nasal congestion, and your dark circles.
It's something to try, at least, if the area under your eyes is darker than usual.
http://lifehacker.com/try-clearing-your-sinuses-if-you-have-dark-circles-unde-1660174413See also:
