Final answer:
Charles may be experiencing Seasonal Affective Disorder (SAD), a mood disorder with symptoms such as increased appetite and sleepiness during winter months. Melatonin, affected by the changes in daylight, plays a role in this condition. Light therapy and vitamin D supplementation may serve as non-drug interventions for SAD.
Step-by-step explanation:
Every year, Charles becomes sad when the days get shorter in winter, but he usually feels better in the springtime. He may be suffering from Seasonal Affective Disorder (SAD). SAD is a mood disorder that often occurs during the winter months, particularly in regions with longer winter nights.
One possible non-drug therapy for SAD is light therapy (also known as phototherapy) which involves exposure to artificial light that mimics natural sunlight, helping to regulate melatonin levels and improve mood. Research has also indicated that a deficiency in vitamin D may contribute to SAD, which is more prevalent in individuals with darker skin pigmentation.