The abbot of Wat Ornoy in Nakhon Pathom province said he had been served with mangosteen juice which he believed had been mixed with poison while leading people in prayer at his temple on Sunday.
The activist monk did not say why he did not go to hospital for treatment and report the incident to police.
In a message posted on his Facebook page, Luang Pu said he felt an immediate burning sensation from his throat to his stomach after he drank the juice, but managed to finish his prayer.
Later he tried to drink a lot of water to vacate his bowels and could not sleep almost all night due to burning pain in the stomach.
He said he felt sick the next day, with a high fever and abdominal distension. The monk said he began to recover only after making himself traditional herbal medicine and taking it along with a stomach protector every two hours. Making a full recovery would take more time, he added.
Luang Pu said he had been aware that some of his rivals wanted him to die after he joined the PDRC's "Bangkok shutdown" campaign in mid-January and led the Chaeng Watthana protest site.
"But don't worry. There will be no second time," he wrote of the supposed poisoning. "I will not die easily."