If one falls asleep while lying down, or falls asleep while leaning on something for support and gets into such a deep sleep that if that support is removed, he will fall – wudhu will break. If one falls asleep while sitting or standing in salaat, wudhu will not break. But if one falls asleep while in sajdah, wudhu will break.
If one is not in salaat and falls asleep while sitting down with his buttocks pressed on his heels and without leaning against a wall or anything else – then wudhu will not break.
While sitting, if one is suddenly overcome by sleep and falls down, then wudhu will not break if the person’s eyes open immediately after falling down. But if even a few moments lapse for the eyes to open, wudhu will break. But if, in the sitting position, the person sways from side to side without falling down, wudhu will not break.
If one falls unconscious, or loses his senses because of insanity, then wudhu will break even if the unconsciousness or insanity was for a few moments. Similarly, if some drug or intoxicant is consumed and one is intoxicated to the extent that he cannot walk properly and his steps are unsteady – then too wudhu will break.