Jonathan Haidt, an associate professor of psychology at the University of Virginia says in his new book, The Happiness Hypothesis, "Happiness has a very weak relation to the events in our lives. Your happiness level is determined mostly by the structure in your brain - not by whether good or bad things happen to you. Negative events hurt or feel bad, but they are not usually as bad as we think and don't last as long as we think."
Still, researchers at the University of Chicago's National Opinion Research Center surveyed 1,340 people in 2004 to find out what problems most negatively impacted their lives. Most of the problems were related to increased incidents of illness and the inability to afford medical care; mounting bills; unemployment.
The inability to afford health care rose from 7% in 1991 to 11% in 2004. Those who said they lacked health insurance increased from 12% to 18%. Link