Does unintentional vomiting violate the fast?
In the Name of Allah the Most Merciful,
No. It does not violate the fasting. This is because the Prophet (swa) said: “Whoever is overcome by vomiting, he does not have to make up that day of fasting and whoever makes himself vomit, he must make up for the day of fasting” (Abu Dawud 2390, Ibn Majah -1676).
Among other things that could happen unintentionally to a fasting person besides vomiting and that do not invalidate the fast are: wounds, nosebleeds and water going into his throat against his will.
Allah knows best.