Answered by Shaykh Ilyas Patel
Does dosing off break your wudu? For example, if I were sitting in class and I started dosing off, would that break my wudu?
In the Name of Allah, Most Merciful and Compassionate
Light dosing, which means to be able to hear most of what is being said around one, does not invalidate wudu. However, one should exercise caution, because one often does not realize that one was in fact sleeping [Haskafi/Ibn Abidin, Radd al-Muhtar `ala al-Durr al-Mukhtar]
Imam Shurunbulali explained that among the things that do not invalidate wudu are:
“ The swaying of a sleeping person in such a way that it is possible that his buttocks may have lifted. It has been mentioned in Abu Dawud that the companions of the Messenger of Allah (Allah bless him and give him peace) use to wait for Isha to such an extent that they use to nod their heads, then pray and not repeat wudhu.
Or one whose buttocks are established upon the earth even though he is leaning upon an object which if removed would cause him to fall.
The reason for this is that ones buttock is firm on the ground and nothing is expected to exit.” (Shurunbulali, Imdad alFattah pg 92)