Sleep, or a lack of it, is proven to be linked to clinical depression. Insomnia is extremely common in the US and affects one out of every three adults at some point in their life. It is more common in older adults (usually due to chronic physical illness) and women (who experience significant hormonal changes throughout their lives). Insomnia is often a key characteristic in diagnosing depression. The inability to get to sleep or to maintain sleep throughout the night is thought to be a key contributing factor to the onset of depression.
When you are sad or feel hopeless because of a personal situation, these feelings can sometimes interfere with sleep as those thoughts spin around your head at a thousand miles an hour. Those feelings can be so overwhelming and persistent that you cannot fall asleep or stay asleep. Sleep is a restorative state where your body and mind recharge from the events of the day. If that state is interrupted, you will feel fatigued, which leads to a lack of exercise and declining fitness level. This can cause a vicious cycle of inactivity and sleeplessness.