Pramono Anung, a member of Megawati's political party, the Indonesian Democratic Party-Struggle (PDI-P), said the former president was admitted to the Metropolitan Medical Centre hospital in Jakarta earlier this week.
"I have seen her twice. She is getting better ... she's just tired and needs some rest," said Anung, adding Megawati could leave the hospital in two days.
Anung denied reports in the Indonesian media that Megawati
was suffering from dengue fever, a mosquito-borne disease that can be fatal.
Hospital officials declined to comment.
Megawati, the daughter of Indonesia's founding president
Sukarno, served three years as president but was defeated last year by Susilo Bambang Yudhoyono in the country's first direct presidential election.
Her PDI-P now leads the opposition to the government in parliament.