Decreased sunlight can cause drops in your body's production of serotonin, a brain chemical that helps to determine mood. Lack of light can also alter the brain's balance of melatonin, a chemical produced during the hours of darkness that helps to govern sleep patterns and mood.

We are affected a great deal by being more tired. And it's very much due to our physiological processes in the body. The sleep hormone we have called melatonin is secreted in the body when it's dark.