Hmmm very interesting. Thanks.

http://www.azumio.com/sleep-cycle-wh...ightest-sleep/

[Waking up in the beginning stages of your sleep cycle is important because our bodies aren’t almost entirely shut down. Being awoken in the middle of REM sleep can cause grogginess that has the potential to last throughout the morning and even throughout the day. This explains why sometimes we sleep for eight or nine hours and still feel like we barely got any rest at all.]