The impact of stress is profound yet greatly underestimated.  Our ancestors had stresses such as physical danger, starvation, plague, etc. but nothing quiet like the stress modern humans face.  Early humans spent most of their time looking for food and resting.  They lived in tribes for protection.  Modern humans are alone in the world and fend for themselves.  The need to perform well to keep a job, keeping up with the neighbors or impressing friends has created an unrelenting cascade of daily stress we often take to bed with us at night.  Daytime exhaustion is a common complaint resulting from stress-altered sleep. This all adds up to twenty-four hours a day of stress that eventually creates the chronic illnesses that lead to our disability and eventual early death.   Stress impacts mood in a negative way.  The inability to control mood is a result of  stress.