Spring fatigue

Why do we feel so sluggish in spring, even though the sun is shining, the flowers and trees are in full bloom, and a warm breeze is blowing? For many people, springtime fatigue makes little sense; after all, the mood should be good when the sun is shining. For some people, however, springtime fatigue is a real problem that can manifest itself in low mood, exhaustion, irritability and even despair.