Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.036.

Section : Loss of consciousness.

This nullifies the ablution regardless of whether it was owing to insanity, fainting, drunkenness, or some medicine. It also does not matter if one was unconscious for a short or long period of time, or if one was sitting, or fell to the earth, and so on. The aspect of unawareness here is greater than that of sleeping. The scholars are agreed on this point.