According to Art Rathbun, biofeedback specialist and counselor at Kansas State University, it's not unusual to feel more worn out during winter, when the lack of sunlight often brings a mood-depressing effect. Fading daylight decreases only a tiny bit of human energy. Rathbun explains that personal winter holiday behavior also affects our need for sleep.
People party more and alcohol consumption goes up.
Many people lose energy because they get less exercise during the winter. The holiday rush contributes even more to dragging feet. Sleep deficits, according to Rathbun, may occur when people lose as little as one to two hours of sleep for a period of four or five days. Don't fear though. A sleep deficit will not be allowed to completely bankrupt the body.