Changes in well being, jet lag and some sleep disorders can occur when one's clock is out of sync. The long days of spring and summer have a natural and obvious effect on energy level. Most of us find that getting up in the summer is easier than in the winter, and we often feel better, more alert, and more productive during the day. After work, we may even have enough energy left over to get some exercise or work around the house. By contrast, the relative lack of light in the winter causes many animals to slow down and conserve energy, even to the point of hibernation.
Many people also experience reduced energy levels in the winter months.
Most of us have trouble getting up and out when it is dark outside, and we may feel lethargic throughout the day as well. The consequences of low energy levels in the winter can be significant. Work and school performance can suffer, resulting in career problems and poor grades. Even personal relationships may undergo higher levels of stress in the winter. Bright artificial light can help make up for a lack of sufficient sunshine in the winter.