People get used to the stress of a busy lifestyle but as soon as they get a chance to rest, their cortisol level drops and the true state of their body comes out. It's why people get sick or feel burned out on vacation.
Sleeping for 12-13 hours is a long time to barely be moving. Think about all the congestion in your body, and in your neck and shoulders.
In the time you're awake you could benefit from some cardio. Anything that gets your heart rate up for about 20 minutes or so. And yeah, good food and hydration will play a role.
If you feel that those 12-13 hours are not productive rest - i.e. you awaken feeling like shit, not really rested - then that falls under the category of an adrenal sign. Bodies that need rest yet can't rest usually do well with schizandra. But address diet and exercise first.