Dear Doctors: I had such a bad attack of vertigo that my boyfriend drove me to urgent care. The doctor got it to go away by having me lie down and then moving my head around. Why did I have that episode of vertigo, and why did that treatment help?

Dear Reader: Vertigo is the sudden onset of a sensation of spinning or whirling. It can feel like the environment around you is in motion, or that your own body is spinning through space. The resulting dizziness can be so intense it often causes nausea.

Most episodes of vertigo arise from problems with the delicate mechanisms of the inner ear, which aid in balance. This is known as peripheral vertigo. Less common is central vertigo, which involves the brain. This classification of vertigo can arise due to physical injury or trauma, migraine, infection, cancer or stroke. Vertigo can also be a side effect of certain medications.

From your description of the treatment you received, it appears you had an episode of what is known as positional vertigo. The full medical term is benign paroxysmal positional vertigo, or BPPV. It is the most common cause of episodes of vertigo. Although it can be extremely uncomfortable -- and often frightening -- BPPV is not life-threatening. However, it can adversely affect quality of life. The dizziness it causes can also increase the risk of falling, which is a leading cause of fractures in older adults.

To understand what happened, we need to talk about the vestibular system. This is a tiny but remarkably complex set of fluid-filled structures, receptors and neural pathways located in the innermost part of the ear. Working together, the components of the vestibular system help you sense motion and detect positional changes. The brain uses this information to calibrate the physical responses needed for movement and balance.

Among the elements of the vestibular system are miniscule calcium crystals, which help convey the sensation of motion. If these crystals become dislodged, tilting the head quickly can cause them to drift out of position. This leads to the delivery of faulty data to the brain, which in turn causes the spinning and whirling symptoms of vertigo.

When your doctor manipulated the position of your head, she was using the Epley maneuver. It is named for the physician who pioneered it. The treatment involves a precise rotation of the head, with the goal of redistributing the dislodged crystals. First, the person’s head is placed in a position that triggers vertigo. They will then lie down and, with the nape of the neck at the edge of the exam table, make a slow 180-degree turn of the head.

The next step is to reposition the body so that it aligns with the head. The person will then be asked to return to an upright position. Although not physically risky, the maneuver can briefly intensify the symptoms of vertigo, and it can cause nausea or even vomiting. In most cases, the Epley maneuver resolves positional vertigo. If not, one or more repeats of the procedure may be needed.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: I have dandruff, and my doctor says it’s from seborrheic dermatitis. Can you explain what that is? I’ve been using the special shampoo I was given, and it helps. When I stop using it, though, the dandruff comes right back. Also, it’s making my hair really dry.

Dear Reader: Dandruff is a condition in which the skin on the scalp begins to flake and shed. It is often caused by a mild form of an inflammatory skin condition known as seborrheic dermatitis.

The word “seborrheic” refers to the sebaceous glands. These are miniscule glands embedded in the skin, almost always alongside a hair follicle. These glands secrete a waxy and oily substance known as sebum. The degree to which someone’s hair is naturally oily or dry is connected to the activity of their sebaceous glands.

When seborrheic dermatitis develops on the scalp, it is referred to as dandruff. It is not a danger to health, and it is not contagious. The most visible symptom of dandruff is the presence of the white flakes that you have described. These are dead skin cells, which become pale and translucent as they are shed. Additional symptoms can include itching on the scalp and areas of thickened, scaly or crusty skin.

Seborrheic dermatitis is often associated with an overgrowth of a genus of fungus known as Malassezia. It is a yeast that naturally occurs on the skin. This type of yeast requires fat for nourishment, which is why it is commonly found near the sebaceous glands. When something causes an overgrowth of the yeast, it can trigger an inflammatory response. Dry or cold weather can lead to flares of dandruff symptoms. So can hormonal shifts, a buildup of hairstyling products or the warm and humid microclimate created by wearing a hat or wig.

Treatment of seborrheic dermatitis on the scalp has two main targets. One is to reduce the colonization of the Malassezia yeast. The other is to manage any symptoms of inflammation that are making the person uncomfortable. When the sebaceous glands of the scalp are overactive, they produce an abundance of sebum. This, in turn, can encourage the growth of the Malassezia yeast associated with dandruff symptoms. When this occurs, modulating sebum production is also an important part of managing the condition.

The shampoo that you have been advised to use contains an antifungal agent that is designed to slow or stop the growth of the yeast. However, because it does not completely eradicate the yeast, ongoing use of the shampoo is necessary to manage the fungal infection. Because reducing sebum production is also one of the goals of treatment, these products can lead to dry hair, as you have experienced. Dandruff shampoos also contain ingredients to ease itchiness and reduce flaking. These shampoos come in a variety of formulas, with different added ingredients. With a bit of trial and error, you can find the brand of shampoo that works best for your specific situation. Some people find using a rotation of different products can be helpful.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: Ads for hydration boosters claim to make one glass of water equal to three glasses of water. These products seem to be primarily water, sugar and salt. I have water, sugar and salt in my diet every day. Does that have the same benefit of the combined solution in the so-called booster?

Dear Reader: You are asking about a vast array of products that, as you point out, promise to maximize the body’s ability to absorb water. Also known as hydration multipliers, they are offered as powders, liquids, tablets, syrups and gels. Unlike sports drinks, which come premixed, hydration multipliers are meant to be added to plain water. Last year, global spending on these products topped $1.7 billion, making the additives big business.

Hydration multipliers typically contain four main ingredients: electrolytes, carbohydrates, vitamins and amino acids. These have important roles in maintaining optimal fluid balance, providing energy and aiding in fluid absorption. The most frequently added electrolytes are sodium, potassium and chloride, each of which is lost when we sweat. Carbohydrates, to be used as fuel, typically take the form of sugars such as glucose, fructose or sucrose. Amino acids are included because they help move water from the small intestine and into systemic circulation for distribution to the tissues. When it comes to vitamins, B and C are common add-ons. The advertising on hydration multipliers claims that the products provide these components in ratios that amplify hydration.

There is no question that drinking enough water is key to optimal health. After all, the human body is about 60% water. We rely on proper -- and precise -- fluid balance in our tissues for digestion, muscle repair, joint health, blood sugar control, heart and brain health, hormone production, organ function, energy, elimination, blood pressure regulation and mental focus.

Many Americans fail to drink enough water each day. This is particularly true for younger people, who drink a lot of sugary sodas, and older adults, who gradually lose the thirst cues that remind them to drink. We do lose electrolytes in sweat, and also excrete them in urine. That said, drinking plain water is still adequate for most of us. If the taste is too boring, many people find that adding a squeeze of citrus, a slice of cucumber or some other natural flavor can help the water go down more smoothly. Unsweetened fizzy water, which also comes with natural flavorings, is another option.

You are correct that when it comes to the electrolytes, amino acids, vitamins and carbohydrates that are contained in hydration multipliers, a balanced diet will provide you with all that you need. Your body will take care of using them in the proper ratios and proportions. That means eating leafy greens, vegetables, nuts, seeds, legumes, fruit, dairy products, certain fish and seafood, healthful fats and lean meats. Unless you’re an elite athlete, you can save the hydration multipliers for those times that you are engaged in prolonged or intense exercise that is making you sweat profusely.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)