Lightheaded, Dizzy and Nauseous After Exercise? Here's What Could Be Happening

If you've ever stepped off the treadmill or elliptical and experienced lightheadedness, dizziness or nausea, you know how concerning it feels and how it can dampen your desire to exercise in the future.

There are a number of factors that can play a role in feeling sick after a workout. Most commonly, feeling dizzy or lightheaded is a result of not being able to get enough blood and oxygen to your brain.

Feelings of nausea after a workout can be caused by not consuming enough calories to compensate for the amount of physical activity you're doing. And intense exercise or overexertion can cause nausea, shaking, weakness and dizziness, per the National Library of Medicine.

Figuring out the source of the problem can help you avoid it in the future, leaving you feeling refreshed and happy you worked out. Here are some potential causes and what you can do to treat and prevent these symptoms.

Working out — particularly doing cardio — is designed to make your heart work harder than when at rest. To do that, you need to start a session gradually to slowly raise your heart rate. And you need to end your workout gradually, too, so your heart eases back to its normal pace.

That gradual end is your cooldown. It gives your body the time it needs to return to normal, including the way it pumps blood through your system. If not, your blood can pool in your legs, causing dizziness and possibly fainting, according to the American Council on Exercise (ACE).

Dehydration can sneak up on you. The harder you work, the more water you'll lose through sweat, which contains not just water, but also essential electrolytes like sodium.

Losing too much water and not replacing it leads to dehydration, while an abnormally low level of sodium in your body can cause a condition called hyponatremia, which includes symptoms like nausea and vomiting, fatigue and headache.

But don't go overboard with water, either. "In extreme cases of prolonged exercise, too much could result in diluting the normal balance of sodium in your body (hyponatremia)," Peng says.

Pushing your body too hard can result in your heart working too hard and not getting enough blood to your head, resulting in lightheadedness or dizziness. Intense exercise also pulls blood away from the lining of your stomach and intestines, which can cause nausea, says Lon Kilgore, PhD, of CrossFit Santa Cruz in California.

Some athletes view these symptoms — nausea, shaking, dizziness or even vomiting — as a badge of honor, according to Kilgore. However, there's no honor in hurting yourself by exercising too much.

Dr. Kilgore reports that intense exercise interferes with your digestive system's functioning, and if you throw up, you expose the lining of your esophagus to harsh stomach acid, potentially damaging it.

"When you exercise, your body draws the energy it needs from glycogen, the readily available form of sugar stored in your liver and your muscles," Peng says. "Not having enough readily available glycogen for your workout could cause your blood sugar to drop."

Having low blood sugar (called hypoglycemia) can cause dizziness as well as irritability and inability to focus. The risk is even greater in people who have diabetes, as the combination of exercise and certain diabetes medications, including insulin, can increase the likelihood of a blood sugar drop.

Sometimes the cause of post-workout dizziness involves the heart. One little-known condition is postural orthostatic tachycardia syndrome (POTS).

It often affects young people born female and causes the heart to race from even minimal exercise — especially if your activity includes changes in position, from reclining to standing up quickly, per the Cleveland Clinic. This can lead to dizziness and even fainting.

Dizziness can also be caused by a condition called benign paroxysmal positional vertigo (BPPV). This vestibular disorder typically comes on suddenly and is caused by movement of crystals in your inner ear.

If you experience lightheadedness, dizziness and nausea directly after working out, there are certain things you can do to immediately help your symptoms subside.

If you feel dizzy, lightheaded or nauseous while exercising, stop immediately. Continuing to exercise while feeling faint could lead to tripping, falling and injuries. Take a break. You may find it helpful to sit down with your head between your knees as you restore blood flow to the head.

Or find an open area where you can lie down on the floor and put your feet up. This will help increase the blood flow to your upper body and head. Sip on a sports drink that contains electrolytes, but don't drink too much too fast.

Talk to your doctor if you are unsure about your symptoms. They can help you determine the cause and find the right treatment plan.