His fast is not invalidated; because it overcame him, so it is excused. The Prophet (peace be upon him) said: "Three things do not break the fast: vomiting, wet dreams, and cupping." In Sunan al-Bayhaqi al-Kabir 4: 220. The Prophet (peace be upon him) also said: "Neither vomiting nor cupping nor having a wet dream breaks the fast," in Musannaf Abd al-Razzaq 4: 213, and Sunan al-Bayhaqi al-Kabir 4: 220. As mentioned in the rule of what breaks the fast, p. 145.