By Elizabeth Goodman Artis for

There's nothing like an intense, sweaty workout to make you feel like a million bucks -- calmer, happier and more comfortable in your skin (and your jeans). But anytime you push yourself physically, especially if it's a tougher-than-normal class or you're getting back into a routine after a hiatus, you may experience a few mild symptoms, especially if you're not properly hydrated. When should you be concerned?

"I tell my clients that the one symptom they should seek immediate attention for is any kind of chest pain or tension in the chest, arm, neck or even back that persists for more than 20 minutes -- it could indicate a heart attack," cautions Tommy Boone, Ph.D., M.P.H., board member of the American Society of Exercise Physiologists and editor in chief of The Journal of Exercise Physiology. Otherwise, here are a five exercise side effects that are okay to experience from time to time, and when to seek medical help.

Mild Nausea Or Headache
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If you push yourself super hard or try a new workout that's extra intense (Crossfit, anyone?) and feel mildly queasy afterwards, you may just be dehydrated. This is true of a headache as well -- any head pain that occurs during a tough workout is likely a sign that you haven't had enough fluid, and it should ease once you take a good, long drink from your water bottle.

When to call your doctor: If it doesn't go away after a few hours after your workout. "You could be fighting off an illness like the flu, and exerting yourself has brought the symptoms to the forefront," says Jason Karp, Ph.D., an exercise physiologist and personal trainer.

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