
"I immediately drafted a letter of resignation and sent it to deputy prime minister Sahas Banditkul before leaving for the hospital," he told the Matichon newspaper in an interview.
It is the first interview he has giving since quitting.
"It is as prime minister Samak says. I had to quit because of my wife's health," he said.
He added his decision was further affected by political tension and the pro and antigovernment faction clashes.
"After one person was killed, I talked with my family about continuing working in the government," he said. The state of emergency was imposed a day before he resigned.
In addition, his secretary Poksak Nilubol's resignation made life difficult, he added.
He admitted a constitutional demand that Parliament be consulted before a bilateral or multilateral deal is signed made his job difficult, too.
"Foreign ministers could be accused of treason if they fail to comply," he said.
Tej said during his tenure he felt pressure from close associates, including people he personally respected. "Some of these people did not speak to him for the 39 days I was in office."
Wife Pensri was under pressure, too, he added. Her niece worked for Tej's predecessor Noppadon Pattama. He said the two had opposite political ideas and the comparison was "unfair".
Tej said former prime minister Samak never pressured him on any decision.