Occasionally your body shoots you the equivalent of a check-engine light—a weird spasm, say, or a sudden, piercing chest pain. Your brain races. Do you hustle to the doctor? Or just ignore it?
Doug Leawood of Kansas City defaulted straight to the doomsday scenario. His check-engine light: He saw red. In the toilet. "I was scared," says Leawood, a 41-year-old insurance rep who was in great shape. "My mind went immediately to colon cancer. I thought I was a goner."


To Leawood's immense relief, blood didn't reappear in the following days, but he was sufficiently spooked to book an appointment right away with his doctor. Before he knew it, he found himself lying on his side in an outpatient surgical facility, counting backward from 10 as a gastroenterologist readied a scope that would snoop around his colon. Leawood checked out fine. No cancer, no worries—just an anal fissure, or small tear up his kazoo. 

But like the driver of the car that screamed "total engine meltdown," Leawood hasn't fully regained confidence in his machinery. Not that any of us have such confidence, given the strange and fleeting pains, spasms, gurgles, and clicks that surprise us at random moments. Are these signs of dangerous underlying conditions, or just harmless blips from a steady state? With help from frontline doctors who've seen it all before, you can sort out which quirks you should take seriously—and which ones you can ignore.

Penetrating Chest Pain
Worst fear: Heart attack
Likely culprit: Muscle spasm or stitch
"This is every man's nightmare," says Reid Blackwelder, M.D., a professor of family medicine at East Tennessee State University. "But if the pain goes away relatively quickly, it's probably not a big worry." Sudden, intense chest pain by itself can simply be a muscle spasm or even a stitch. It might also be pre-cordial catch syndrome—a very intense, sharp pain, typically in your left chest, that may feel like a heart attack to its unsuspecting victims. It's harmless, has no known cause, and can last for just a few seconds or up to several minutes. It's more common among children and teens but does occur occasionally in young men.

But combine intense chest pain with shortness of breath, nausea, dizziness, and/or sweating, and you might indeed be facing a heart attack. "As a general rule, when pain of any kind persists, you need to pay attention," Dr. Blackwelder says. Call 911, and chew two 81-milligram aspirin tablets to thin your blood and ease its flow to your heart.

Twitching Eyelid
Worst fear: ALS, a.k.a. Lou Gehrig's disease
Likely culprit: Eyelid spasm
"I see this all the time," says Charles Cutler, M.D., an internist in Norristown, Pennsylvania, and chairman of the American College of Physicians board of governors. Patients frequently think a twitching eyelid is an early symptom of something horrible, he says—like ALS, a progressive, degenerative disease that affects nerve cells in the brain and the spinal cord. "But while it's uncontrollable and certainly annoying, the twitching is generally benign," Dr. Cutler says.

The medical term for this is blepharospasm. It's simply the result of uncoordinated muscle contractions in your eyelid. These spasms tend to come out of nowhere and occur every few seconds for a minute or two; episodes can occur for up to several weeks. Doctors aren't sure of the cause, although stress, fatigue, and caffeine may be culprits.

Buckling Knee
Worst fear: Major joint damage
Likely culprit: Weak quads
A knee can buckle so swiftly you'll be looking for the sniper who shot you. But the pop or crunch you hear is due to a "reflex inhibition" of your quadriceps. "It's a protective reflex—the same one that occurs when you step on a tack," says Sherwin Ho, M.D., director of sports medicine fellowships at the University of Chicago medical center. "Your quad is looking to protect a painful knee by keeping weight off it."
The wobbliness is most likely a sign that the shock-absorbing cartilage under your kneecap has worn down—a condition that can lead to patellofemoral pain syndrome, says Dr. Ho. The fix: stronger quads, which take stress off your knee by acting as shock absorbers.

To build your quads, start with short-arc extensions, says physical therapist Jason Amrich, C.S.C.S., director of the Boulder Center for Sports Medicine in Colorado. Lie on a mat with a rolled-up towel under the thigh of your injured knee. Straighten your leg, hold for 5 seconds, and lower. Do 10 reps, twice a day.
To reduce patellofemoral pain, work your gluteus medius—a hip muscle that helps move your thigh—with clamshell exercises. Lie on your side with your back against a wall, hips stacked, and hips and knees bent 45 degrees. Keeping your heels together, raise your top knee toward the ceiling, opening and closing your legs like a clamshell. Do 15 to 20 reps and switch legs. Complete 2 or 3 sets every other day.

Severe Headache
Worst fear: Brain tumor
Likely culprit: Tension or cluster headache
"Everyone thinks they have a brain tumor whenever they get a sudden, intense headache," says Dr. Blackwelder. "Despite the many brain tumors we see on TV, they really aren't all that common." What's far more likely, he says, is that it's simply a severe headache—a migraine, a tension headache, or a cluster headache.

Migraines produce severe, throbbing pain, often on one side of your head. They're also frequently accompanied by nausea and sensitivity to light. Another clue: People who suffer from migraines tend to first experience them before they reach their 20s. So if you're over 40 and have never had a migraine, you probably have a tension or a cluster headache. A tension headache produces dull pressure or tightness across the forehead, while a cluster headache includes sudden, severe pain, typically on one side of the face, usually surrounding the eye.

Brain tumor symptoms often vary with the tumor's size, location, and growth rate, but morning headaches tend to make doctors nervous. If you repeatedly wake up with headaches, see your physician to rule out a tumor. Do the same if you have a headache that worsens with sneezing, coughing, or any exertion, all of which increase the pressure within your head.

Underarm Pain
Worst fear: Lymphoma 
Likely culprit: Muscle spasm
Sharp underarm pain that comes and goes is probably the result of a muscle spasm or pleurisy, a medieval-sounding term for inflammation of the tissue that lines the chest cavity and covers the lungs. Pleurisy is usually caused by an infection, and betrays itself when the armpit pain is sharp and most pronounced when you take a deep breath. Massage and slow stretching can relax spasms, while nonsteroidal anti-inflammatory drugs can limit pain.

If the pain in your underarm is dull and you detect a small, tender knot in the area while feeling around, then your lymph nodes may be swollen. This happens routinely when you're battling an infection. Swelling could also be a sign of lymphoma, though the chance of that is very, very small, says David Ellington, M.D., medical director of the Rockbridge Area Free Clinic in Lexington, Virginia. Have your doctor check out any knots, bumps, or persistent pain.

Blood in the Toilet
Worst fear: Colon cancer
Likely culprit: Hemorrhoids or anal fissure
If you spot bright red blood swirling in the bowl or on the toilet paper, you're probably dealing with hemorrhoids or an anal fissure, especially if the area is painful or tender. An anal fissure, which sounds worse than it is, is just a small cut in the lining of the anal canal. A fissure can develop when you pass a hard or large stool, and it typically heals by itself. (Deeper, chronic fissures may need surgical repair.)

Dark-colored blood mixed with your stool, on the other hand, may indicate a source farther up the gastrointestinal tract, says Dr. Ellington. If any bleeding appears without pain during bowel movements, then you may have a colon polyp or perhaps an internal hemorrhoid. The occasional tarry or black stool (digested blood is black) indicates bleeding in the upper GI tract, perhaps due to a peptic ulcer. Call your doctor, who may schedule a colonoscopy to find the source and rule out colon cancer.