Also for your reading pleasure...

"Studies have indicated that self-described morning people have shorter circadian rhythms than self-identified night owls. This means that morning people sleep through their peak hour of sleepiness, so they wake up feeling refreshed. Evening types usually wake up right around their peak hour of sleepiness, so they may have high levels of melatonin and feel groggy. No wonder it’s tough to rouse them."

Full Article here:
http://www.divinecaroline.com/article/22189/55286-truth-night-owls-morning