Car Accidents Caused by a Medical Emergency: The Sudden Medical Emergency Defense

Drivers who experience a “sudden medical emergency” may be able to avoid liability for a car accident.

By , Attorney St. John's University School of Law
Updated by Stacy Barrett, Attorney UC Law San Francisco
Updated 1/27/2023

Medical emergencies can happen anywhere—at home, at work, at the gym, and even on the road.

We've all seen horror stories in the news about drivers who crash their vehicles into houses or storefronts after having a stroke or a heart attack. These types of situations disrupt our typical responses—emotional and legal—to car accidents. Certainly, the grandmother who ended up with a car where her kitchen table used to be isn't to blame for the accident. But the driver who lost consciousness behind the wheel isn't necessarily to blame either, at least not in the same way that a distracted driver who runs a red light is to blame for a car accident.

Many states allow drivers who lose control of their vehicles for medical reasons to use the "sudden emergency defense" to defend themselves against insurance claims and car accident lawsuits. In this article, we'll cover the ins and outs of the defense and ways to counter it.

What Is the "Sudden Medical Emergency" Defense?

All drivers have a duty to exercise reasonable care on the road, including the duty to keep their vehicles under control at all times. But what happens when a driver loses control because of a sudden and unexpected medical emergency?

Most states recognize a "Sudden Medical Emergency" defense (sometimes called an "Act of God" defense), which limits drivers' liability for car accidents caused by a medical emergency. The reasoning behind this defense is that a driver who suffers a sudden medical emergency isn't really at fault for a resulting accident and shouldn't have to pay for injuries and losses (called "damages").

The sudden emergency defense applies only if the driver responded to the emergency as a reasonable person would have under similar circumstances and only if the emergency was truly unforeseeable.

Proving a Sudden Medical Emergency

The sudden emergency defense is somewhat controversial. Most, but not all states, allow some variation of it. The exact requirements for raising the defense vary by state, but drivers typically must show the following elements:

  • the driver suddenly became physically incapacitated
  • the incapacity wasn't reasonably foreseeable, and
  • the incapacity caused the driver to lose control of the vehicle.

Let's take a closer look at a few of these elements.

What Is a Sudden Physical Incapacity?

Drivers who fall ill while driving and continue to drive are not suffering from a sudden medical emergency. To successfully raise a sudden emergency defense, a driver must have had no opportunity to respond to the medical emergency in time to avoid the accident.

Drivers who experience symptoms of a medical emergency have a duty to pull over to the side of the road rather than continue to drive and put others at risk. When symptoms are present and ignored, the medical emergency isn't "sudden.".

What Is a Reasonably Foreseeable Medical Emergency?

According to the National Highway Traffic Safety Administration (NHTSA), most drivers involved in crashes caused by medical emergencies were aware that they had a medical condition prior to the crash. Drivers who know about a medical condition associated with a crash prior to the crash can't raise the sudden emergency defense.

Drivers who have been medically advised not to drive or who have experienced episodes of incapacity have a duty to stay off the road to keep other people safe from harm. For example, if a driver suffering from epilepsy was medically advised by his doctor not to drive, and got into an accident after having a seizure behind the wheel, he would likely be liable for the injuries and losses he caused. His seizure was entirely foreseeable based on his diagnosis and his doctor's warning. But if he experienced a seizure for the very first time while behind the wheel, he may be able to successfully raise a sudden emergency defense and avoid liability if his seizure caused a car accident.

Other examples of drivers who probably wouldn't make it over the foreseeability hurdle include drivers with a history of heart problems who have a heart attack behind the wheel and diabetic drivers who pass out behind the wheel after not eating all day.

Who Pays for Damages When a Medical Emergency Causes a Car Accident?

In most car accident cases, the driver who is at fault for an accident pays for accident-related losses like vehicle damage, car accident injuries, and lost income. But who pays when an accident is caused by a sudden loss of consciousness or capacity?

In most states, drivers who can prove that an accident was caused by a sudden, unforeseeable medical emergency aren't legally responsible for the accident even if they plowed into someone else's car or living room. When a driver successfully raises this defense, the people harmed by the incapacitated driver must rely on their own insurance to cover their losses, just as they would if an uninsured driver hit them. Incapacitated drivers, of course, must also rely on their own insurance to cover accident-related bills and losses.

Similarly, in the dozen or so states that follow a"no-fault" car insurance system, everyone involved in the accident would first turn to their own personal injury protection to cover expenses regardless of who was at fault for the accident.

In the few states that don't recognize the sudden emergency defense, traditional rules of negligence and fault for an accident apply.

Examples of Sudden Medical Emergencies

In a study published in 2009, NHTSA found that 84% of drivers in crashes precipitated by medical emergencies experienced:

  • seizures
  • blackouts, or
  • diabetic reactions prior to the crashes.

Less common examples of medical conditions that could leave a driver incapacitated include:

  • heart attack
  • stroke
  • aneurysm, or
  • choking.

According to NHTSA, older drivers had a relatively higher percentage of crashes caused by medical emergencies when compared to young and middle-aged drivers. Fortunately, these types are crashes are rare. Only 1.3% of all drivers included in NHTSA's study had a medical emergency while driving and most were involved in single-vehicle crashes.

If you suffer a medical emergency and cause an accident, you should immediately notify your insurance company. You should also, of course, talk to your doctor about your condition and whether it's safe to continue to drive.

Strategies to Defeat the Sudden Medical Emergency Defense

Crashes involving sudden and unforeseeable medical emergencies are rare, but that doesn't mean insurance companies won't try to use the defense more often to deny your claim.

Let's say you're rear-ended in a run-of-the-mill car accident. You collect your medical records and bills and submit a claim to the at-fault driver's insurance company expecting a quick settlement. Instead, your claim is denied. The other driver's insurer says that he isn't liable because he was blacked out at the time of the accident. What do you do?

You don't have to take the other driver's word for it. Remember, the burden is on the driver claiming medical incapacitation to prove the defense. Your strategy to defeat a medical emergency defense will likely focus on three issues.


Is the other driver telling the truth? What, if any, evidence can the driver point to support his self-serving claim that he blacked out before he rear-ended you?


This is a key issue in every medical emergency case. Was the other driver on notice that he was at risk for sudden incapacitation? Was he aware he had a health condition that could cause blackouts? Had he been warned by a doctor about the possibility of blacking out? Had he experienced blackouts before the accident?

You, ideally with the help of a car accident lawyer, will have to carefully review the other driver's medical records to develop this potential line of attack.


Did the driver experience symptoms with enough time to pull over before the medical emergency? In other words, how "sudden" really was this incapacitation?

Just as importantly, did the incapacity actually happen before the collision? For example, did a driver suffers a heart attack before an accident or as a result of the accident?

The answers to these questions about credibility, foreseeability, and timing will determine whether you can overcome a driver's sudden emergency defense and get compensation for your accident-related economic and noneconomic losses.

Talk to a Lawyer

Car accidents involving sudden medical emergencies are tragic and legally complex. If you've suffered a medical emergency while driving, you probably don't want to pay for a car accident that was entirely out of your control. If you've been harmed by an allegedly incapacitated driver, you're probably wondering if the driver truly was suffering from a medical emergency and whether the driver should have been on the road at all.

You may think that you can represent yourself in any car accident claim or lawsuit, but some cases require the skills and knowledge of an attorney. If you're on either side of an accident involving a sudden medical emergency, talk to a lawyer.

A lawyer can help you gather the information necessary to prove—or counter—a sudden emergency defense. A lawyer can also help you negotiate a fair settlement and advocate for you in court if your car accident case goes to trial.

Learn more about how car accident attorneys get paid. When you're ready, you can connect with a lawyer directly from this page for free.

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