Longitudinal studies have shown that people's self-reported levels of happiness are usually not significantly lower than prior to experiencing a trauma. However, chronic smoking and alcoholism have been found to be strongly anti-correlated with happiness, and people often report feeling lower levels of happiness on their birthday.
The Harvard Happiness Project has found that the self-reported levels of happiness of people who suffer from trauma aren't significantly lower than their pre-trauma levels after a year or so, but chronic smoking and alcoholism are strongly anti-correlated with happiness, and family members of people who are chronic smokers/alcohol users result in lower levels of happiness, especially if they don't smoke or consume alcohol.