Psalm 110:3 (New Living Translation)
....and your strength will be renewed each day like the morning dew.
Fatigue is one of the common reasons for spiritual and natural despondency. There are times when a saint is so busy and stressed out that it may simply not be possible to rest. Both the Lord Jesus and the Apostle Paul are classic examples for saints who sometimes went sleepless. It's in such times that the Holy Spirit empowers a saint in ways no natural tonic can. Relying completely on the Holy Spirit during such times makes us more powerful and intimate with Christ.