Dizziness. A pounding heart and a racing pulse. Sweating. These are symptoms of severe hypoglycemia (low blood sugar), and for the estimated 3 million Americans living with Type 1 diabetes, preventing it from happening is a life-or-death priority. Unless you check your blood sugar level and take something to raise it, you’re at risk of lapsing into a coma in less than an hour.

Obviously, that’s a lot of stress to live with. But with dogs trained to detect the dreaded sugar low, people with diabetes have an ever-ready, always-reliable ally in managing this disease. Hypoglycemia alert dogs have their best friends’ backs, using their amazing sense of smell to sniff out low blood sugar –- and to warn them (or, if the diabetics are children, their parents) well before it reaches that critical low point.

So, to the list of astonishing things dogs do for human health — lowering blood pressure, reducing stress, detecting cancer — add sniffing out low blood sugar in diabetics. It’s time for an appreciation of these astonishing dogs, who give their people the confidence needed to face everyday challenges most of us don’t think twice about. Driving long distances, for instance, can be hugely stressful for a diabetic, but with a medical-alert dog along for the ride, it’s a different story.

No one appreciates this more than Dogs4Diabetics founder Mark Ruefenacht, who lived in fear for years. But having diabetes didn’t stop him from becoming one of the country’s top forensics technical experts. In his downtime, the lifelong dog lover volunteered as a puppy raiser for Guide Dogs for the Blind, bringing up 20 puppies who would later undergo training as assistance dogs.

As a volunteer group leader, Mark often traveled with dogs-in-training to help prepare them for various situations like crowded airports. In 1999, Mark brought a black Lab named Benton on a business trip to New York City, where he had a hypoglycemic episode at his hotel and Benton was very insistent in helping him get up.

The experience of having his life saved by a pup made Mark wonder how dogs could help diabetics. From that “aha!” moment came his Dogs4Diabetics nonprofit. In the German language of Mark’s Swiss ancestors, his last name means “alert in the night.” He feels privileged to work at a calling that seems fated from birth.

Today, a black beauty named Danielle is Mark’s guardian angel. Here’s how she and her canine colleagues work: When she scents chemical changes in Mark’s breath and sweat, she alerts him by taking the bright-yellow bringsel attached to her collar and holding it patiently in her mouth like a flag until he acknowledges her.

If a minute passes and she goes unnoticed or ignored, the dog doesn’t give up; she’ll nudge him with her snout, and in true “Lassie, get help” spirit, she won’t hesitate to seek out someone else whenever necessary. Hypoglycemia cannot be detected by the human nose, but incredibly, trained dogs can pick up a sugar low from as far away as 20 feet.

The dogs at Dogs4Diabetics come from Guide Dogs for the Blind and Canine Companions for Independence. After 18 months of training, dozens of dogs don’t make the cut; the dealbreaker might be a fear of escalators. Historically, career-change dogs have been adopted out as pets to families on a long waiting list. But advanced training isn’t necessary in a pet dog, who never gets to use it. “We’re taking all that training and building on it, so the effort wasn’t wasted,” Mark says.

D4D dogs are in no way also-rans — in fact, the quirk that disqualifies them from guide work often indicates a great talent for alerting. Take Armstrong, one of the guide Labs Mark raised from puppyhood. “He was assigned to a blind person, but he was returned after a couple of days because he rearranged her shoes, and you can’t do that to a blind person,” he says. However, Armstrong’s playful spirit — his favorite reward was a game of tug — turned out to be an asset. He was Mark’s own medical-alert dog, beloved friend, and the handsome poster boy of D4D until he sadly passed away in February of aggressive nasal cancer.

When dogs arrive at Dogs4Diabetics’ Nylabone Training Center in California, they do about four months of post-graduate study. Developed by Mark, the regimen incorporates elements of clicker, search-and-rescue, and scent-detection training. “It’s all positive-reinforcement, reward-based training,” he emphasizes.

Dogs go through scent-discrimination trials — picture an obstacle course of scents, including human perspiration from actual diabetics plus a range of deliberately distracting smells, from mouthwatering (steak) to aversive (eucalyptus oil). Each time dogs recognize the smell of a sugar low, they get praise, then a treat.

The dogs are trained to detect sweat, but they work off of breath. “Molecularly they are the same components, but with sweat there’s a 15-minute delay,” Mark explains. When a lifestyle match is made (high-energy humans are paired with high-energy dogs, for example), clients come to the training center for a 16-weekend course in handling their new best friend.

By equipping talented animals for a lifetime of service, Mark says he’s achieved his life’s goal of giving back. “I’m not particularly religious,” he concludes, “but I do believe in living a good life so I can get to Labrador heaven!”

A dog saved his life once — now he’s helping save dogs as well as his fellow diabetics. “By taking career-change Guide Dogs and repurposing them, we’re actually promoting shelter-dog adoption, because we’re saying your local animal shelter is the best place to go for a family pet.”

Do you know of a rescue hero — dog, human, or group — we should profile on Dogster? Write us at dogsterheroes@dogster.com.