During the night as bed time approaches your body temperature naturally begins to go down to prepare your body for sleeping.
Your body at night also begins to lose some body heat naturally which is meant to help you get a good nights sleep although for some people they still don't get enough sleep.
As morning approaches and you get ready to wake up your body temperature begins to rise again to normal levels which helps to prepare you for the day.
The rise in your body temperature also helps you to wake up again as well.
During the night your body temperature starts to drop at least 1 to 2 degrees from your normal daytime body temperature and then in the morning your body temperature rises again to it's normal temperature.