My Pilates instructor is a fan of telling my group fitness class, “Breathe or you’ll die.” Sure, it sounds obvious: You need oxygen to survive. Breathing is 100 percent in your best interest. But, unfortunately, the process of breathing is not always as simple as inhaling and exhaling. Think about it: How often do we have to remind ourselves, or perhaps others, to “take deep breaths” when we’re anxious or sad or overwhelmed?

When the body is under duress, it often experiences something called “effortful breathing.” The breathing muscles contract, and there are generally higher levels of muscle tension throughout the body. The more we need air, the more we have to remind ourselves to get it. This effortful breathing is in contrast to relaxed breathing, during which the muscles work primarily during inhalation, but are relaxed during exhalation. At one extreme, you could consider it your “hanging out on the couch, watching TV” breathing.

It’s almost ironic—the body needs more oxygen delivered to the muscles when we exercise, and yet we’re wired to make this process more difficult for ourselves. There are some who think this effortful breathing can be used to our advantage during workouts—weight training, specifically—through something called the Valsalva maneuver (basically what you do when you try to pop your ears on an airplane). Performed by forcibly exhaling while keeping the nose and mouth closed, this is cautioned against by many physicians, although the reports of its dangers for weight lifters remain unconfirmed.

On the flip side, there are times when anxiety can make you feel breathless, even though you’re taking in extra air. It all comes back to our fight-or-flight response. In anticipation of the fight or flight, we automatically breathe faster, hoping the extra oxygen will help us to move faster or fight harder. But we’re not actually in danger—not any that’s immediate, anyway—so we’re left there, breathing too quickly, or hyperventilating.

When we’re hyperventilating, many think it’s because our bodies are responding to a lack of oxygen. Rather, we lack carbon dioxide because we’re breathing out more carbon dioxide than we have a chance to create. Although doctors still debate whether it’s the lack or excess of CO2 that causes the initial hyperventilation, the end result is our brain (tricking us yet again) making us think we need to get more oxygen into our bloodstream—even though we already have plenty. Slowing down our breathing is one solution here, and it’s where that whole “take deep breaths” thing comes back into play.

The way we breathe is inextricably tied to the way we live our lives, with a huge impact on our physiology and health. “You can influence asthma; you can influence chronic obstructive pulmonary disease; you can influence heart failure," Mladen Golubic, a physician in the Cleveland Clinic's Center for Integrative Medicine, told NPR. “There are studies that show that people who practice breathing exercises and have those conditions—they benefit.”

So the next time you’re stressed or anxious, remember that Anna Nalick song from 2004 and “Breathe, just breathe.”