Once in a while you will find that you just cannot get going.
You try to work in different places but your body does not respond. You eat different types of food or drink coffee or eat some sugary stuff to get the energy to buckle down and start working, but you find the rejuvenation short-lived.
When this happens your body is telling you it is time to rest and have a lazy day. If this happens too often then there would be a cause for worry. However, if it is once a month it is fine. When you go full speed for many days your body will tell you it is time to refuel by resting a bit.
It boils down to balance. There is a time to work and a time to play and a time to pray. Just like we have seasons in the year similarly we have seasons in our life journey. Enjoy the ride no matter what.