Say when you are "born" you are supposedly happy-- but then as you grow older you may get depressed, sad, sick, all sorts of mental illnesses. So, just being very brief here:
1- Drug addicts/Alcoholics/etc - use drugs/drink to go from depressed to HAPPY/FEEL GOOD. Not talking about frat dudes and kids that are generally overall happy and not addicts, just recreational users.. I mean serious hardcore addicts.
2- Go to therapist/psychologist/psychiatrist to "talk" about why you have been down and blue, depressed, etc etc.. You talk to the therapist to gain understanding/take anti-depressants to get back to happy.....
in 2008 so many people have to take medication just to function in society.... Mentally im speaking. Maybe you are supposed to be depressed/sad but we strive for anything to make us happy.