If you don’t get enough sleep, you could end up “functionally drunk” in just days, a new study claims.

Many people often burn the candle at both ends, neglecting sleep for other priorities and apparently underestimating just how important sleep is. And you don’t have to undersleep by that much: even if you’re getting six hours of shut-eye every night, you are actually building a sleep debt, according to a University of Michigan statement.

Middle-aged men are typically the most sleep-deprived of everyone. Women on average tended to go to bed earlier and wake up later, especially between the ages of 30 and 60.

Additionally, people who spend more time outside and in the sunlight tended to go to bed earlier and get more sleep than those who stayed inside all day.

At a certain point — sometimes just a few days — people who build up a sleep debt eventually become functionally drunk. This results in a significant drop in performance, but at the same time the brain gives you a false impression that things are getting done just fine.

Researchers used a free smartphone app to reduce jetlag to come to their conclusions, collecting data on thousands of people in 100 countries.

“Across the board, it appears that society governs bedtime and one’s internal clock governs wake time, and a later bedtime is linked to a loss of sleep,” Daniel Forger, who holds faculty positions in mathematics at the U-M College of Literature, Science, and the Arts, and in the U-M Medical School’s Department of Computational Medicine and Bioinformatics, said in the statement. “At the same time, we found a strong wake-time effect from users’ biological clocks–not just their alarm clocks. These findings help to quantify the tug-of-war between solar and social timekeeping.”