The number one reason why most people either have difficulty falling asleep or have difficulty staying asleep is stress. Stressful feelings throw our hormonal system and nervous system out of sync, making it challenging to calm down and creating difficulties sleeping.
Our bodies are well adapted to dealing with acute stressors, but chronic stressors, not as much. Our society lives in a very sympathetic dominant state. We, more or less, live in fight or flight mode. The things that we stress over now are things like money, raising kids, school, family, relationships, work and driving on the interstates.