Have you ever felt dizzy and light-headed? Chances are the answer is yes. About 50% of adults experience dizziness at some time in their lives.

Feeling dizzy isn’t just uncomfortable. It can be dangerous—for example, if you fall or lose control of your car while driving.

There are many different causes of dizziness or vertigo (the feeling that you or the world around you is spinning), so it can be tricky to figure out what’s triggering your symptoms.

Here are the five most common causes—and important clues to determine which one is affecting you. Many causes of dizziness aren’t serious, but some are, so it’s always a good idea to get checked by your doctor.

Benign paroxysmal positional vertigo (BPPV). Millions of tiny crystals, or otoliths, are attached to hair cells in the inner ear. They bend the hairs when you change position, which tells the brain that you’ve moved. When you have BPPV, the crystals break free and float into a part of the ear where they’re not supposed to be. Result: A bout of vertigo that usually lasts 60 seconds or less.

Important clues: Suspect BPPV when the attacks occur only after you’ve moved your head…there’s a delay of three to five seconds between the head movement and the vertigo…and the severity decreases when you have multiple episodes over a period of minutes or hours.

What to do: Ask your doctor to recommend a therapist who can show you how to do the Epley maneuver. Named after its originator, it consists of five steps that can eliminate symptoms in about 80% of patients. Other maneuvers practiced by therapists also can work.

The Epley maneuver includes reclining on a bed or table and then, in very particular ways, tipping your head to both sides, rolling over on your side and then sitting up, which causes the crystals to return to their usual location. Videos are available on YouTube.com.

Ménière’s disease. No one knows what causes Ménière’s disease, although it’s been linked to autoimmune diseases, viral infections, head injuries and other conditions. It causes intense dizziness, nausea and vertigo when a buildup of ­endolymph fluid in the inner ear causes pressure changes that interfere with ­balance.

The episodes come and go. Some people have attacks every few days. Others go weeks or months between attacks. Some people are lucky and have just a single attack—but this is rare.

Important clue: Hearing loss in one ear that mainly affects lower frequencies (such as difficulty hearing a man’s voice). This is the opposite of normal, age-related hearing loss, which usually affects high frequencies first.

What to do: Reducing fluid in the inner ear is the cornerstone of ­treatment. Some patients can achieve this just by consuming less sodium. The FDA advises limiting sodium to no more than 2,300 milligrams (about one teaspoon daily of table salt). But most patients also will need to take a diuretic (sometimes referred to as a “water pill”) that helps your body get rid of unneeded salt and water through urine. These include acetazolamide (such as the brand Diamox) or hydrochlorothiazide (such as the brand HydroDIURIL).

It’s helpful to give up caffeine. Caffeine reduces blood circulation in the inner ear. Also, cut back on alcohol and sugar—these can increase dizziness in some people. Reducing stress can help, too. We don’t know why, but stress can trigger attacks.

Acoustic neuroma. This is a benign tu­mor that grows at the base of the brain and can affect a variety of nerves including the auditory nerve. About 3,000 Americans are diagnosed with one of these tumors every year. The symptoms include dizziness, a loss of balance and nausea.

The tumors aren’t cancerous, but they can cause serious impairments and even death if they grow large enough. They typically grow about 2 mm (about one-eighth of an inch) a year.

Important clue: Slight hearing loss (usually in one ear), along with the other symptoms mentioned above. Some patients also experience tinnitus, ringing or buzzing sounds in the affected ear.

What to do: Because the tumors are slow-growing, your doctor might decide just to track your progress with periodic MRIs, especially if your symptoms are minor. But there’s always a risk that a tumor will cause permanent hearing loss, along with damage to the facial nerve or other structures in the brain. If your doctor is concerned that an acoustic neuroma is dangerous, he/she will probably recommend either surgery or radiation to remove or shrink it.

Orthostatic hypotension. Almost all of us have experienced the occasional dizziness that occurs when we stand up too quickly. For some people, these episodes happen often—this is particularly true for the elderly…those taking blood pressure medication…and people with certain conditions (including heart disease or Parkinson’s disease).

What happens: When you stand up, blood is pulled downward and away from your brain. It takes about a minute for your body to adjust to the change in position by increasing the strength of your heartbeat and tightening your blood vessels. In the meantime, a lack of circulation and oxygen to your brain can make you feel dizzy.

Important clue: Suspect orthostatic hypotension when you experience dizziness or light-headedness only when you’re changing position—usually when you go from a seated or lying position to standing.

What to do: See your doctor. Orthostatic hypotension, while itself relatively harmless, can be caused by cardiovascular or nervous system disorders that are serious and require treatment. If you are on blood pressure medication, the dosage may need to be adjusted.

Whatever the cause of orthostatic hypotension, it helps if you change ­positions slowly to give your body time to adjust. Example: To get out of bed, swing your legs off the bed and sit up…but don’t stand up yet. Wait a minute for your blood pressure to stabilize. Then stand up slowly.

Dehydration. You might not think that skimping on fluids could cause your head to spin, but it’s not uncommon.

What happens: When you don’t drink enough water, your blood volume falls. Reduced blood volume can reduce the amount of blood that circulates through the brain. The result can be dizziness or even fainting spells. Older adults are particularly at risk because the sense of thirst declines with age.

Important clues: People who live in hot climates or take diuretics (the ­“water pills” often used to treat high blood pressure) are particularly prone to dehydration.

What to do: Drink plenty of water throughout the day—and sip even when you aren’t feeling particularly thirsty. Eight glasses a day is a good amount to shoot for. If you’re taking a diuretic, ask your doctor whether switching drugs or changing doses might be helpful.

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