The reason why "Sleep" is on several different singles, is because Garbage's record companies released the first album singles in a different order for each country. It was first on the UK Only Happy When it Rains in Sept 95, then on the European and Australian Queer in Oct 95, then on the USA Only Happy in January 1996. Phew!
well, i've got it on the "queer" single (european/german version?). sucks that their former labels released several versions of the singles including different track lists... anyway, "sleep" is one of my favorite b-sides.