For most of her adult life, Isobel Johnson missed out on a lot of sleep. Last year it got so bad that she would fall asleep at the wheel and couldn't pay attention at work.
"It got progressively worse and I would be sleepy in the day time," said Isobel.
Sleep apnea stopped her breathing hundreds of times a night. But for decades, she got by.
Researchers recreated what was happening to Isobel in a three week study. Scientists kept nine people on a grueling wake-sleep cycle. For every 32 hours of being awake they got ten hours of sleep. This is similar to someone who gets about five and a half hours of shuteye a night.
Sleep medicine expert Dr. Bob Abrashimi at Good Samaritan Hospital says the study revealed that at certain times of the day, people can function well but the body can't continue that way indefinitely.
"Their performance was getting worse as days went on," said Dr. Abrashimi.
In the study, people with chronic sleep loss performed the best between 3 p.m. and 5 p.m. Researchers say that's when the brain secretes the least amount of the sleep hormone melatonin.
"During this high circuit in the late afternoon, they can have misleading performance," said Dr. Abrashimi.
The findings offer important safety implications not just for shift-workers like truck drivers, medical personnel and rescuers but for the roughly one in six Americans who don't get enough sleep.
"If this becomes a chronic habit, once this chronic habit continues for days or weeks, that's where these patients get into problems," said Dr. Abrashimi.
A CPAP machine, which is prescribed to treat sleep apnea, has done wonders for Isobel.
"Get some help, because I think a lot of people don't realize that it's a medical condition," said Isobel. "Help is available."
While Isobel is doing better scientists say it is unknown how fast the body recovers after being sleep deprived for so long. The National Institutes of Health says adults need seven hours to nine hours of sleep for good health.