Presidential spokesman Martin Andanar said the throbbing headache would have made it difficult for Duterte to concentrate amid the overwhelming barrage of summitry.
Andanar was unaware if Duterte's absence in the meetings had anything to do with a reported miscarriage suffered by his daughter, the mayor of their southern Philippine city of Davao.
Duterte has been in the news because of intemperate remarks he made about President Barack Obama ahead of the summit.
Duterte later walked into the venue of the Association of Southeast Asian Nations' summit meetings in Vientiane, about four hours late but just in time to catch the start of the East Asia Summit, which groups the leaders of the 10-nation ASEAN and eight other heads of state, including President Barack Obama.
Obama and Duterte shook hands and briefly chatted at a holding room Wednesday night before a gala dinner.
One of Duterte's Cabinet members, Jesus Dureza, said he asked the Philippine president about his discussion with Obama. "It was OK," Dureza quoted Duterte as saying. "He told me, 'We can talk some more at another time.
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