Sudden death: warning signs you shouldn’t ignore

Published on 1 March 2026

Chest pain, breathlessness and dizziness may be early signs of cardiac arrest. Knowing when to seek help could save a life.

At a glance

• Sudden death is often preceded by warning signs that appear before a person collapses.
• Cardiac arrest frequently unfolds in phases, creating opportunities to intervene earlier.
• Prompt medical attention and swift action by bystanders during a cardiac arrest can save lives.

It can happen to anyone — a sudden heaviness or tightness in the chest, pain that spreads to the shoulders or arms, and unexpected difficulty breathing.

Within minutes, that person may collapse. And, if medical help does not arrive in time, death can follow, leaving loved ones asking how this could have happened so quickly.

This tragic phenomenon, in which someone dies suddenly and unexpectedly, is known as Sudden Unexplained Death (SUD). It is most commonly linked to cardiovascular conditions, including heart attacks.

Alarmingly, projections suggest that the incidence of heart attacks in Singapore could rise substantially in the coming years, from about 480 cases per 100,000 people in 2025, to around 1,400 per 100,000 people by 2050.

While the term “sudden death” suggests that it happens without warning, the reality is that it rarely comes out of nowhere. According to Dr Benjamin Leong, Senior Consultant with the Emergency Medicine Department at National University Hospital (NUH), there are often warning signs before a collapse.

The phases of cardiac arrest

The symptoms that precede a sudden cardiac arrest can be looked upon in terms of phases.

The first phase is before there are any symptoms at all. This is when people feel well, but may already carry risk factors that increase the likelihood of sudden cardiac arrest. 

These include cardiovascular disease and its associated conditions such as unhealthy cholesterol levels, diabetes and high blood pressure. Structural heart disease, abnormal ECG patterns, and a family history of heart conditions also raise risk.

“At this stage, the focus is on prevention,” said Dr Leong. “That means controlling modifiable risk factors and screening individuals who may be at higher risk.”

The next phase is when the underlying disease begins to develop, and symptoms may start to surface. These can include chest pain, breathlessness, unusual fatigue or dizziness.

“These symptoms should never be ignored,” stressed Dr Leong. “They need to be evaluated promptly so that treatment can be started early, reducing disease progression and the risk of sudden cardiac arrest.” 

The third phase in sudden cardiac arrest can happen just moments before the event.

“In most patients who suffer an out-of-hospital cardiac arrest, many experience sudden, severe chest pain or breathlessness anywhere from a few hours to a few minutes before the event,” said Dr Leong.

“Patients should seek medical help immediately if they experience these symptoms. They should not wait or delay, as we have seen cases where patients lost consciousness shortly after the ambulance was called.”

Can sudden death affect ‘healthy’ people?

While rare, SUD or cardiac arrest can occur even in individuals who appear healthy, exercise regularly and maintain a balanced diet.

Among young adults, potential causes include abnormalities in the heart’s electrical conduction system, structural heart disease, inflammation or infection of the heart, aortic dissection, and certain respiratory conditions.

In older adults, coronary artery disease and its risk factors are more common, although strokes and other non-cardiac causes can also occur without warning.

“Some of these conditions are inherited,” noted Dr Leong. “When a sudden unexplained death occurs, screening family members for inherited conditions is very important.”

Bystanders can save lives

When sudden cardiac arrest strikes, survival often depends on what happens in the first few minutes. That is why the actions of bystanders who witness a collapse can be lifesaving.

“The person who has collapsed will not be able to help himself or herself,” said Dr Leong. “Even the fastest ambulance in the world cannot reach the patient faster than the bystander standing right next to them. That bystander is crucial. Call 995 immediately and follow the instructions of the dispatcher.” 

Dr Leong also encouraged the public to learn cardiopulmonary resuscitation (CPR) and how to use an Automated External Defibrillator (AED), as these skills can make the difference between life and death. Members of the public can attend a DARE (Dispatcher-Assisted first REsponder) course or the DARE Plus Programme by the Singapore Civil Defence Force, and download the myResponder app to become a Community First Responder.

“Sudden cardiac arrest cannot wait until the patient reaches hospital,” he added. “Through close collaboration between the community and emergency services in the pre-hospital chain of survival, we can give patients their best chance.”

In consultation with Dr Benjamin Leong, Senior Consultant, Emergency Medicine Department, NUH.