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.

Most of the scholars are of the view that it is not obligatory to do Wudu after drinking camel's milk.

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.