Answered by Shaykh Amjad Rasheed
If a fasting person faints during the day, is his fast still valid?
If one faints, the fast is not broken, unless he remains unconscious all day. This meaning that if a person faints before Fajr time enters, after having made the intention to fast, and he remains in this state all day until after sunset, then his fast is invalid.
However, if he is only unconscious for part of the day, his fast is not broken, even if it was for most of the day. Imam Nawawi said in the Minhaj, “The more apparent (azhar) position is that the unconscious person’s fast is not harmed if he awakes for only a moment during the day.”
Amjad Rasheed
[Translated by Sr. Shazia Ahmad]