This has been an ongoing debate between me and some of the other gamers locally. The spell "Sleep" causes the following condition to be applied to affected targets "helpless".
The spell states on pg 344 " Sleeping creatures are helpless." It also states "Sleep does not target unconscious creatures".
Some members of the local PFS have decided that sleep must make you "unconscious" and "prone" seeing as to how that is what happens in the real world. This seems to make sleep more powerful then it is written. It is written to only render a person "helpless", not "unconscious" and "prone". It would seem to me that the spell is not designed to have you drop your weapon and go prone with all that is implied by the condition of "unconscious".