Therese Coffey said she “nearly died” because of the stress of being a minister.
The former environment secretary resigned from her job as Prime Minister Rishi Sunak reshuffled his Cabinet on Monday.
Ms Coffey, the Conservative MP for Suffolk Coastal, revealed how tough she found being in government telling her local BBC radio station: “Nearly five years ago I got so ill, I nearly, dare I say it, died.”
She held previous cabinet roles, including two months as both secretary of state for health and social care and deputy prime minister under Liz Truss.
During a frank interview, Ms Coffey told BBC Radio Suffolk: “I was in hospital for a month with some of the stresses that happen with ministerial life.
“A few years ago I certainly worked myself into the ground somewhat, but I learned a lot from that incident and that’s why I’ve always had a joy about life.”
In a letter to the Prime Minister, she said that it was “now the right time to step back from government”, adding: “I look forward to supporting you from the backbenches and working together for a Conservative majority at the next election, which I believe to be profoundly in the national interest.”
Mr Sunak thanked Ms Coffey for “years of dedicated ministerial service and your friendship to me personally”.