The Gallup-Healthways Well-Being Index's Emotional Health Index score is based on Americans' self-reporting of positive and negative daily emotions, as well as self-reported clinical diagnoses of depression.
Gallup and Healthways began tracking daily emotions in January 2008.
The U.S. Emotional Health Index score was 79.9 last month, slightly above the previous high of 79.8 recorded in March 2008 and May 2010.
Americans scored better on all 10 of the Emotional Health Index measures in April than they did at the low point in September. Self-reported "enjoyment" has also increased.
The percentage who said they experienced enjoyment a lot during the previous day rose to 85.6 percent in April, up from the three-year low of 83 percent in September.
The findings are based on approximately 30,000 telephone interviews with U.S. adults conducted each month from January 2008 through April 2012. Americans were asked whether they felt, or did "a lot of," each of the following the day before the survey: Smiling/laughing, learning/doing something interesting, being treated with respect, enjoyment, happiness, worry, sadness, anger and stress.
The survey's margin of error was 0.6 percentage points.