(CBS) With more and more Americans saddled to their computers and cell phones, workdays are getting longer and people are losing sleep.

A new survey finds Americans are struggling to stay awake at their desks … and even behind the wheel.

That trend can be tragic.

Every day, retired professor Thomas Callagy re-lives the night his wife was killed, and blames himself.

“The van flipped over and she was killed instantly,” he said.

Callagy was behind the wheel, and fighting fatigue, when he fell into what he calls a “micro-sleep.” A few seconds was all it took for the car to veer off the road.

“I was completely devastated because as far as I'm concerned, I killed my wife,” he said.

What happened to Callagy is tragic, but not that surprising when you look at the latest statistics from the National Sleep Foundation. Its new study finds that one out of three Americans have dozed off at the wheel.

“It's very difficult for us to voluntarily stop sleep,” explained Dr. Anan Krieger of the NYU Medical Center. “Sleep is a mechanism that's intrinsic to our body.”

The study blames the epidemic of sleepiness on longer workdays, which often continue late into the night, resulting in an average of just six hours and 40 minutes of sleep on week nights.

“Some people might be able to get around with just four hours of sleep and be quite productive,” said Dr. Krieger. “Others — and we see them very often — may need about 10 to 11 hours.”

Of those polled, 29 percent say they've been very drowsy at work, or have even fallen asleep, and twelve percent report being late to work in the last month because they were sleepy.

Thomas Callagy says he's never forgiven himself for the mistake that killed his wife, and hopes his story will be a wakeup call to drowsy drivers who think it will never happen to them.