Every parent has been there: your baby is crying, crying, crying, and nothing you do can make her go to sleep. Then inspiration strikes: let’s put her in the car and drive around until she nods off. And, like magic, it works!

It works so well, in fact, that it’s tempting to think that a car seat might just be your child’s favorite, and best, place to nap. Even if you haven’t actually resorted to nightly drives to soothe your kids to sleep, we’ve all heard the jokes about the phenomenon, and we’ve all been on long rides where the fussiest anti-sleepers have nodded off almost instantly.

While we certainly sympathize with sleep-deprived parents, and while we know that long road trips are often necessary, the reality is that allowing your infant to nap in her car seat is actually incredibly dangerous— and one mom has the tragic story to prove it.

Lisa Ellor Smith of Aledo, Texas is mother to 18-month-old daughter Mia. One day while Lisa was at work, she received a call from the long-term and trusted babysitter currently watching Mia— and tragically, it was the call of every parent’s nightmare.

ABC channel WFAA 8 reports:

“I got a call while I was at work,” her mom, Lisa Smith, said. “Worst call I’ve ever had in my life. ‘Drop everything. Mia didn’t wake up from her nap.’”

Mia’s cause of death was what’s called positional asphyxia, which happens when a person’s breathing is restricted by their position.

And that cause of positional apsphyxia? The babysitter put Mia to sleep in her car seat. Experts theorize that Mia likely slumped down in her seat, cutting off her airway and subsequently suffocating.

New York City Administration for Children’s Services explains:

Because babies don’t lie flat in car seats, they can suffocate when their heads (which are very heavy compared to the rest of their bodies), tip forward, blocking their airway. These products are not made for babies to sleep in and are dangerous because babies are not sleeping flat on their backs.

It is tragic that more people aren’t aware of this danger, and absolutely horrific that Mia and her mother had to pay the ultimate price for that ignorance. So let’s honor Mia’s memory, and spread the word – as her mother continues to do – so that no other child has to suffer the same.

To hear the warning from brave mother Lisa Smith herself, watch her courageous interview with CNN’s Headline News below.

Do you regularly put your baby in a car seat to nap? Did you know about the dangers? Have you always taken car seat safety seriously, or were you one of the eye-rolling people Lisa describes in her interview?