(CNN)Living with a plugged nose isn't fun, but James Nestor was ready. Plus, it was for science.
While researching his recent book, "Breath: The New Science of a Lost Art," Nestor let Stanford University scientists block his nostrils with silicone and surgical tape to measure the impacts of breathing through his mouth for 10 days.
"We knew it wasn't going to be good, because there's a very firm scientific foundation showing all the deleterious effects of mouth breathing, from periodontal disease to metabolic disorders," Nestor said. The surprise was just how quickly the experiment affected him.
Nestor's blood pressure rose 13 points, edging the writer into stage one hypertension. Measurements of heart rate variability showed his body was in a state of stress. His pulse went up, and he stumbled around in a mental fog.
He also snored for hours each night, developing obstructive sleep apnea. His blood oxygen levels dropped.
"We had no idea it was going to be that bad," Nestor said. "The snoring and sleep apnea was so dramatic, and it came on so quickly, that everyone was pretty floored."
What Nestor learned, aside from the hazards of being a research subject, was that mouth breathing can ruin a good night's sleep.
Breathing through your mouth at night puts you at higher risk for sleep disorders including snoring, sleep apnea and hypopnea, the partial blockage of air, scientists have found. Each of those, in turn, can lead to daytime fatigue.
That doesn't mean you're doomed to wake up in a daze because you're prone to mouth breathing when you sleep. Experts have a long list of strategies designed to turn you into a nasal breather — including a low-cost breathing hack you can pick up at the corner store.
What causes nighttime mouth breathing?
There is a long list of reasons why people breathe through their mouths at night, said Dr. Steven Park, a surgeon with a specialty in sleep medicine, and the host of the podcast, "Breathe Better, Sleep Better, Live Better."
"The most common reason is if your nose is stuffy," Park said. "From allergies, or if you have a deviated septum. Lots of medications can also cause nasal congestion."
Those problems are aggravated by lying down, he explained.
"Generally when you lie down the blood vessels inside your nose fill up with blood," he said, explaining that the rush of blood causes swelling and constriction. If you can't breathe easily through your nose, you're likely to open your mouth for air, Park said. That triggers a positive feedback loop.
"You would think that if you open your mouth you would breathe better, but actually the reverse happens," he said. Opening your jaws causes the tongue to slump backward, obstructing your airway. "Even if you don't have sleep apnea, or you have mild sleep apnea, opening your mouth makes it much, much worse."