Former British marathon number one Mark Steinle had a disastrous return to action in Singapore after three years out of competition because of injury.
Steinle has suffered ill-health in recent years
The 31-year-old, who was the fastest Briton in the 2002 London Marathon, was reduced to walking as he clocked a time of three hours 15 minutes.
"I think it was heat exhaustion. I was drinking lots, but bringing it back up again almost immediately," he said.
"I thought about dropping out 100 times but I was part of a team."
He said his problems continued after the race, and he would have to reassess his plans if he wanted to be a serious contender for next year's London race.
"I came back to the hotel and was shivering and throwing up for a couple of hours, but I feel better after a sleep. I just wasn't prepared," he said.
"I've only been training a few weeks. I've got to put a lot more work in if I'm going to be ready for London next year."
Steinle picked up an Achilles tendon injury at the 2002 Chicago Marathon and the problem has troubled him since.
He had an operation on the injury in 2003, which forced him to take a year off.
Then he was troubled by scar tissue from the operation tugging on his calf muscle, which troubled him throughout 2005.
He returned to training last summer.
Kenyan Amos Matui won the race for the second year in a row, breaking his own course record with a time of two hours 15 mins 01 secs.
Compatrior Salina Kosegi won the women's race, again in a course record time of 2:31.55.