This hypothesis focuses on how disruptions to the body's circadian rhythm, driven by melatonin, affect the patient. During winter, as sunrise gets later, people begin waking up before dawn, so their body produces melatonin and drives their circadian rhythm later even though they are awake. For other people, an earlier sunset means their body produces melatonin too early before sleeping. Both of these situations can cause depression, fatigue, and sluggishness in the patient.