Is too much hygge time the reason you’re feeling run-down?

Admit it, sometimes you’re secretly glad when a friend breaks plans to hang out. Between a crazy work schedule and nonstop notifications on your phone, it’s no surprise that silence and alone time have become the ultimate luxuries. And while the occasional night in can be 100 percent necessary, a new study might discourage you from making it a habit.

Researchers at the University of Pennsylvania want you to know that too much isolation can lead to poor sleep—and other health problems. In one study, the cells of fruit flies legit changed when they were separated from their fly squad. Okay, yes, fruit flies definitely aren’t people, but the authors of the study found that in virtually every animal species, too much alone time actually stresses out cells, potentially causing long-term health problems.

“When you keep animals isolated, it basically induces a disturbance of sleep, which then gives rise to cellular stress.”

“Ultimately, [the head researcher] realized that keeping animals isolated induces a cellular stress response,” says senior author Nirinjini Naidoo, PhD, a research associate professor of sleep medicine at Penn. So yes, too much solo time might ultimately lead to adrenal fatigue. “When you keep animals isolated, it basically induces a disturbance of sleep, which then gives rise to cellular stress,” he adds.

But unless you’re headed for shut-in status there’s really no reason to freak out: As long as you’re getting some social interaction throughout the day, a night in is totally justified. How else will you squeeze in that oh-so-important tub time (with a face mask on)?

If you’re all the sudden inspired to socialize, here’s how to make friends at your next workout. Or, you can try the Tinder for friendship.