If the sleep is light and the sleeper can feel it if he breaks his wudu, then sleeping does not break wudu whether the sleeper is lying down, sitting, leaning on something or sitting without leaning.

Touching impure things does not break wudu, but if a person touches something impure, it is not permissible for him to pray until he has washed it off.

Passing wind breaks wudu but if a person passes wind continually, he has to do wudu for each prayer when he wants to pray, then if wind comes out of him whilst he is praying, that does not invalidate it.