The 70-year-old, who was stabbed in the abdomen during an election meeting in 2018, was in the northeastern state of Rio Grande do Norte when he began to feel unwell "connected to the knife attack", according to a party representative.
Bolsonaro, Brazil's president between 2019 and 2022, has had recurring health problems due to complications from the knife attack and has undergone several operations.
The former president has been banned from running in the 2026 presidential election, but still hopes for a comeback and would have started a tour of Rio Grande do Norte on Friday.
In late March, Brazil's highest court announced that Bolsonaro will be put on trial for attempting to instigate a coup after the 2022 election defeat.
