What is the ruling on the fast of one who swallows phlegm in their throat while feeling nauseous, and is قضية (recompense/making up the fast) incumbent upon them, and what should they do in this situation?

If a fasting person expels phlegm, resulting in the expulsion of stomach fluids, there is no sin upon him and his fast is not invalidated if he was unaware that this would invalidate it. However, if he intentionally expels phlegm knowing that it will cause stomach fluids to be expelled, then this invalidates the fast, unless he is compelled to do so, such as if his illness necessitates vomiting. In this case, he is permitted to vomit and break his fast, and he may eat and drink for the rest of his day, because his breaking of the fast was due to an excuse.