I guess it’s root is duša (soul). My parents gave it to me because it’s popular both here, in Serbia and in Slovakia, although it’s pretty rare among Slovaks here. It’s fairly popular among the Serbs, probably because of the most famous Dušan, emperor Stefan Uroš IV Dušan of Nemanjić dynasty aka Dušan the Mighty.
btw English speakers have pretty hard time pronouncing it for some reason. That clear, short u becomes all kinds of sounds.