Seasonal affective disorder is not simply “winter blues,” but a biologically driven condition caused by reduced light exposure and circadian disruption. Shortened daylight alters melatonin, serotonin, and cortisol signaling, leading to fatigue, low mood, sleep disturbance, and cognitive slowing. When recognized early and treated with targeted light therapy, vitamin D repletion, and circadian-based interventions, seasonal affective disorder is highly manageable and often fully