You’re tired, busy, and the couch is calling your name. Nice try, but those are fairly flimsy excuses for skipping a workout.

However, there are legitimate reasons for sitting out a day or several.

“Sometimes your body may need time to heal or rest,” says Moira McCarthy, M.D., an orthopedic surgeon specializing in sports medicine at the Hospital for Special Surgery in New York City.

That’s when powering through your usual workout could set the stage for illness or injury. How can you tell if you need a break? These six reasons warrant a rest day.

1. You’re coughing or wheezing.

If you’re just fighting mild cold symptoms, like a runny nose or scratchy throat, moving may boost your circulation and help you feel better.

“Just make sure that you do something low-intensity and don’t push your body too hard,” says Jessica Matthews, an assistant professor of exercise science at Miramar College in San Diego and senior advisor of health and fitness education at the American Council on Exercise.

But if the symptoms are below the neck, like in your chest, the coughing, wheezing or difficulty catching your breath could signal a more serious infection and definitely gives you an excuse for staying in bed until you feel better.

2. It’s past midnight, and you’re planning to hit the gym at 6 a.m.

Don’t pat yourself on the back for dragging yourself out of bed on 5 hours of sleep. Cutting your slumber short, even for exercise, may do more harm than good.

Research shows that even one night of sleep deprivation can affect your health: It raises levels of stress and hunger-inducing hormones. Make it a regular habit, and you’ll increase your risk for a number of conditions, including heart disease.

“If you can, switch your workout to that afternoon or evening,” says Matthews. “Or make an effort to sneak in more movement throughout your day, like taking a walk during lunch.”

3. You’re running a fever.

A high temperature is an instant stop sign. That’s because exercise can raise your internal temperature, which can slow the body’s healing process.

If you show any signs of the flu, such as chills or body aches, send yourself to bed instead of the treadmill.

4. Your muscles still hurt from yesterday’s—or the day before’s—workout.

That’s a sign of delayed-onset muscle soreness (DOMS). A tough workout causes tiny tears in muscle tissue. That’s good, because the repairs will make you even stronger.

However, exercising with stiff, aching muscles can compromise your form.

“You may favor one side during a movement, or not be able to go through a full range of motion,” says Matthews.

The result: You’re more likely to hurt yourself.

If only one part of your body, say your legs, are complaining, you can work your arms instead. But if you’re sore all over, hang up your sneakers for a day or two.

5. Your knee or foot aches every time you go for a jog.

“Persistent pain is a red flag that something’s wrong,” says McCarthy.

You could be sliding into or already have a strained muscle or overuse injury, such as plantar fasciitis or even a stress fracture.

McCarthy suggests resting the area until you can exercise pain-free. If the problem persists, see a health care provider, such as a physical therapist.

6. You’ve been running on empty for weeks now.

This is different from feeling sluggish or tired for a day or two: Exercise can boost low energy levels. If you’ve been battling nagging fatigue for 2 weeks or more, see a physician before heading to the gym.

“You need to rule out a more serious medical issue, such as a thyroid problem or chronic fatigue,” says Matthews.

The article The Only Good Reasons to Skip Your Workout was orginally published by our partners at Prevention.com.