You’re halfway through your workout when your head starts pounding. It’s the dreaded exercise headache—and it can seriously derail your workout.

Getting a headache from working out can be a real buzzkill. If you’re dealing with head-throbbers when you want to be focusing on making gains, there are a few things you need to know (Wake up with a headache instead? Here are 8 things your morning headache is trying to tell you).

First, here’s why exercise headaches happen in the first place.

A lot of times when you’re working out, the exercises cause you to bear down, like when you’re stabilizing your core doing an overhead press This is called the Valsalva maneuver—it’s the same thing you use when you poop—and it boosts the pressure inside your abdomen.

“That in turn is transmitted into the head via the jugular veins causing an increase in intracranial pressure—which can lead to a headache,” explains Michael Cutrer, M.D., a neurologist who specializes in headaches at the Mayo Clinic.

Also, your body releases adrenaline and other chemicals that make your heart beat faster. Your breathing increases, too. If you are susceptible to headaches, an abrupt change in your internal biochemical environment—like adrenaline or an increase in blood pressure or heart rate—activates your already hyper-reactive head pain system.

A typical, harmless exercise-induced headache feels like mild pressure or throbbing, and often affects both sides of your head. It can start during or just after strenuous exercise, with the onset occurring gradually over the course of several minutes to an hour, says Dr. Cutrer (Here are 7 signs your headache isn't normal).

Both cardio and lifting can trigger headaches in susceptible people. So who’s at risk?

“Sustained physically strenuous exercise is the most common trigger,” says MaryAnn Mays, M.D., a headache specialist at the Cleveland Clinic. “Working out in hot conditions also puts people at risk, particularly if dehydration occurs or there’s a lot of humidity.”

Other risk factors include working out in particularly bright light or sun, feeling fatigued, or having low blood sugar or a history of migraine headaches. Patients with chronic neck pain or injury might also experience exercise-induced headaches, Dr. Mays says.

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In most cases, exercise-induced headaches are not serious. They usually subside in less than six hours, though they could last for 48 hours post-exercise, says Dr. Mays.

But in rare cases, an exercise-induced headache can be deadly.

If the onset is sudden within seconds or what is called a “thunderclap,” with the maximum intensity occurring within a minute of onset, see a doctor immediately, she says.

This more serious type of headache is symptomatic of a ruptured aneurysm, which can cause blood leakage, a powerful activator of pain fibers, and lead to a severe headache, says Dr. Cutrer (Here's how to spot a brain aneurysm before it's too late).

It can be accompanied by vomiting, loss of consciousness, neck rigidity, and neurological symptoms like double vision and problems thinking of the correct word. Those kinds of symptoms warrant immediate medical attention.

If you’ve been experiencing frequent headaches while exercising—even if they’re not the severe kind—you still might want to loop in your doctor, too. Your clinician might do imaging of the brain and blood vessels to look for aneurysm or a tumor, among other issues.

Dr. Cutrer says that once it is clear that you do not have an aneurysm, your doctor could also recommend taking a non-steroidal anti-inflammatory (NSAID) like naproxen sodium (Aleve) one hour before exercising. They block inflammatory compounds in your body called prostaglandins, which are responsible for the pain.

Other ways to ward off headaches while you’re working out? Make sure to get in a good warmup before you start with the intense stuff, like sprints or lifting heavy. Doctors aren’t sure why this helps, but it can cut your risk of developing a headache. Other prevention strategies include sticking to a healthy sleep schedule, limiting caffeine or alcohol, eating regularly prior to your workouts, and drinking plenty of water (For more health news delivered right to your inbox, sign up for our Daily Dose newsletter).