Whilst writing the Harry Potter books, J.K.Rowling was experiencing harrowing personal issues and suffered from depression. The Dementor's Kiss is supposed to represent how mental illness can make you feel. It's very sad to know that people who are suffering from mental illness can describe it as being like a Dementor's Kiss. Thank goodness for hope and happiness in the world, which JK portrays as a defence against these monsters through the bright light of the Patronus.