The feverish teen's heart was already pounding as he lay in the ambulance.
But before he could get medical attention at the hospital, the ambulance was involved in a collision with a van on the Pan Island Expressway (PIE).
The crash caused a heart monitor to fall and hit his chest, adding breathing difficulties and chest pains to his symptoms.
The 14-year-old, who wanted to be known only as Timothy, was en route to KK Women's And Children's Hospital (KKH) on Sunday morning for an abnormally fast heart rate and a temperature of 39.8 deg C.
The accident occurred in the middle of three lanes at about 1am.
In heavy rain, the ambulance collided with a van that had allegedly braked suddenly on the Paya Lebar Flyover.
Timothy's 26-year-old brother, who wanted to be known only as Kevin, told The New Paper: "When he felt like he was being flung forward, he grabbed onto the wire of the heart rate monitor mounted on a shelf in the ambulance and it fell on him."
Mr Kevin, who was with Timothy and a paramedic in the back of the ambulance, said he was more shocked with the collision than the monitor falling on his brother.
When Timothy complained of how much his chest hurt, Mr Kevin said he "felt pain for him".
"We put him in the ambulance with two injuries but now he had more," he added.
Timothy complained of dizziness and vomited at 11.30pm after a jog with his friends at Bedok Reservoir Park. They had been preparing for a running event the following day.
Worried, Timothy's family called the Singapore Ambulance Association (SAA) and paramedics arrived at 11.40pm to take him to hospital.
On the PIE, a white van ahead of the ambulance was in the middle lane.
Mr Kevin recounted: "Suddenly, the van braked. The ambulance driver told us to hold on tight as he was forced to brake as well."
The ambulance collided with the van.
Mr Kevin had some bruises as a result of the collision.
The van had also collided with the right side of a black car shortly before it braked, said the driver of the car, Mr Javier Low, 20.
His girlfriend was in the car with him at the time of the accident.
The couple did not suffer any injuries.
Mr Low said the van had slowed down after it drove over a puddle, allowing his car to catch up before the collision.
The car had dents and scratches.
The Singapore Civil Defence Force was alerted about the accident at 1am on Sunday and dispatched two ambulances to the scene.
The van driver was taken to Tan Tock Seng Hospital.
Timothy was admitted to the Intensive Care Unit at KKH.
Doctors said he suffered chest trauma from the impact of the heart rate monitor falling on him, said Mr Kevin.
But he added: "Timothy is better now, so I am relieved."
The teen was moved to a normal ward yesterday.
Mr Kevin is heartened by the help rendered by the SAA medical personnel. "They probably suffered bruises like me, but they still attended to my brother," he said.
Police investigations are ongoing.
This article was first published on May 24, 2016. Get The New Paper for more stories.