While dizzy spells can be uncomfortable, it probably won’t surprise you to learn that occasional dizziness is very common in adults. But you may not have suspected that vertigo — a related but more serious condition that makes you feel like the room is spinning as you stand still — is also common, affecting nearly 40 percent of people over age 40 at least once in their lifetime, according to the University of California San Francisco Medical Center. So, how do you know if you have vertigo or ordinary dizziness? The main difference is vertigo can cause nausea and vomiting — and may be a symptom of a serious balance disorder — while dizziness simply makes you feel momentarily unbalanced. That said, dizzy spells can range in severity from merely annoying to seriously debilitating. Here’s what causes vertigo and general dizziness — plus what to do if you experience one of these episodes. Though BPPV is the most common inner ear–related balance disorder, it affects only about 1 out of 1,000 people per year, according to the Vestibular Disorders Association (VEDA). And while it can affect adults of any age, this type of vertigo primarily affects older adults. Most cases occur for no apparent reason, but BPPV has been linked to trauma, migraines, inner ear infections, diabetes, and osteoporosis. After treatment, 50 percent of patients may experience the problem again within five years — especially if it was the result of trauma, say experts at VEDA.

2. Your Ear’s Balance System Controls Blood Flow

“We’ve learned that our inner-ear balance system contributes to the control of our blood flow," says Whitman, “and that the inner ear has the ability to know which way is up.” When you move from lying down to standing up, two inner ear structures, the utricle and saccule, detect gravity. They tell your cardiovascular system to direct blood flow to accommodate your change in position, says Whitman. When that process goes awry, it may cause dizziness.

3. Low Vitamin B12 Levels Can Cause Dizziness

Deficiencies in this essential vitamin may lead to a number of neurological problems, including feeling off-balance, and having low blood pressure and decreased blood flow to your brain, says Whitman. “Vitamin B12 deficiency is easy to detect and treat, but is an often overlooked cause of dizziness,” he notes. Ask your doctor about having a simple blood test to check your B12 levels if you’re having dizzy spells. Good sources of vitamin B12 include meat, dairy products, and fortified breakfast cereals.

4. Dizziness May Be a Symptom of Heart Disease

One simple cause of dizziness is sudden movement, like when you get up too suddenly from your seat or bed. But sometimes dizziness is a sign of a heart condition. Among the cardiovascular-related causes of dizziness are leaking or narrow heart valves, arrhythmias like atrial fibrillation, and atherosclerosis, says Patricia Blau, PhD, associate professor of physical therapy at the University of Texas Southwestern Medical Center in Dallas. These can cause dizziness because they reduce blood flow to the brain, according to VEDA.

5. Migraines Sometimes Cause Vertigo

“It surprises some people to know that dizziness is commonly linked to migraine disease, either with or without headaches,” says Debara L. Tucci, MD, an otologist, neurologist, and ear surgeon at Duke Medicine in Durham, North Carolina. Other symptoms of migraine-related vertigo include sensitivity to motion, light, and sound, adds Dr. Tucci. About 40 percent of people who have migraines experience dizziness or vertigo, according to VEDA.

Many people who experience dizziness, especially people in their twenties, may also have anxiety, says Whitman. “They usually don’t want to hear that dizziness can be linked to anxiety because it suggests that it’s all in their heads,” he notes. “But what’s in your head is your brain. And anxiety can reflect a brain function disturbance that’s possibly genetic.” Compared with people who don’t have anxiety, people with anxiety disorders appear to sway more when subjected to a moving visual environment, Whitman says. And they sway in a way that seems to be synchronized with the visual movement. “These people may be abnormally sensitive to visual stimulation, because their dizziness can increase when they’re watching moving objects or walking through a large, bright store,” says Whitman. This is called visual dependence, and little is known about how common it is. “We need to develop better tests of visual dependence, and we need laboratory tests for what we now call anxiety disorders," ways Whitman. “It’s likely that in the future, these disorders will be reclassified, in part, based on genetics.”

7. A Boat Ride or Waterbed Can Cause Dizziness

It’s pretty common to experience a rocky, dizzy feeling on your first day back after a cruise, says Carol Foster, MD, director of the balance laboratory at the University of Colorado Hospital in Aurora. “For a few people, this feeling, called mal de debarquement, can last for months or even years,” says Dr. Foster. Some 75 percent of all sailors can experience such dizzy spells. Airplanes, cars, and trains can also cause a wobbly-legs feeling. Even relaxing on a waterbed can cause dizziness.

8. Dizziness and Vertigo May Be Side Effects From Medication

So many drugs can cause dizzy spells that there are too many to even list, says Whitman. “That said, high doses of blood pressure medication can cause dizziness, especially in older adults and in people who have started a dose that’s too high for them,” says Whitman. “In my dizziness clinic, I tend to start people on ultra-low doses of medication. Sometimes, less is more.” Check to see if any drugs you’re taking may include dizziness, vertigo, or loss of balance as possible side effects by speaking with your pharmacist or physician. “A careful review of medication lists, and looking for opportunities to decrease dosages, can sometimes yield surprising benefits,” Whitman adds. “Don’t think that you shouldn’t take a medication just because dizziness could be a potential side effect. Most people don’t experience the side effects a drug may cause.”

9. Your Diet or Dehydration Could Make You Dizzy

Even mild dehydration may be why you’re feeling dizzy or light-headed, according to the American Heart Association (AHA). Dehydration can also cause blood pressure to drop, which can lead to dizzy spells, notes the AHA. Dieting can also result in feelings of dizziness, because some diets cause dehydration, says Dr. Blau. According to the AHA, mild dehydration that follows the loss of just 1 to 2 percent of your body weight can cause dizziness.

10. There Are Several Less Common Causes of Dizziness and Vertigo

Pay attention to all bouts of dizziness, because along with other symptoms, they could point to something more serious. See your doctor to rule out health problems related to frequent or severe bouts of dizziness or vertigo. “Even though less than 1 percent of my patients have a life-threatening or previously unsuspected cause of dizziness — such as stroke warning symptoms or a brain tumor — I still take all cases of dizziness seriously,” says Whitman. If you have a brain tumor, it’s usually not the only symptom you have, he says. One very rare condition linked to vertigo is Ménière’s disease. “If you have prolonged episodes of whirling vertigo along with hearing problems in one ear, it could be Ménière’s,” says Whitman. He estimates that this affects only about 0.2 percent of the population, and is sometimes found in adults between the ages of 40 and 60. Though it can’t be cured, it can be treated.