Like most wealthy Zimbabweans, Mr. Mugabe goes abroad for better medical care than he can get at home. That narrows the circle of Zimbabweans who are truly informed about his health — and it means that every time he flies, especially on extended or unannounced trips outside Africa, the rumors fly as well, often claiming that he has died or is at death’s door.

“There will never be a thing called a vacuum, so if the officials are not giving information, rumors will fill the vacuum,” said Tendai Biti, the president of an opposition party, the People’s Democratic Party. “The feelings of uncertainty are a byproduct of a very unstable environment created by the president himself.”

“But this is not unique to Zimbabwe,” added Mr. Biti, who served as finance minister in a coalition government from 2009 to 2013. “Mobutu used to die so many times. In Uganda, Idi Amin used to die so many times. In China, Chairman Mao used to die so many times. In Russia, how many times did Brezhnev used to die?”

This time, the speculation about Mr. Mugabe seemed to have more foundation than usual. He had been scheduled to go to Ghana in mid-August to receive a lifetime achievement award from the Millennium Excellence Foundation for helping to liberate Zimbabwe, but canceled the trip at the last minute.

When he resurfaced several days later at an agricultural show, his appearance merely fanned the flames. He seemed to stumble at one point and was apparently wearing slippers rather than shoes with his suit.

Mr. Mugabe appeared to bounce back, flying to Kenya on Aug. 26 for a conference, followed by a meeting in Swaziland. After that, however, UM1’s movements began raising alarms in some circles. The plane left Swaziland a day before the conference ended, spent three hours in Harare and then took off again for Dubai, arriving on the morning of Aug. 31.

Days of silence ensued. The government said only that Mr. Mugabe was in the Middle East on official business. The Sept. 1 headline on the independent newspaper NewsDay read, “Mystery Over Mugabe Trip.”