How can I tell if my daughter has a concussion?

DEAR DOCTOR K: Last week my 14-year-old daughter fell while skateboarding. She hit the back of her head and was dazed and had blurry vision for a few seconds. But she felt fine once she sat down and rested a bit. Now the left side of her head hurts, but otherwise she feels normal. Should she see a doctor?

DEAR READER: Yes, she should. In a child, particularly, it is often hard to know when trauma to the head may have caused a brain injury. That's why you should never ignore a head injury, no matter how small it seems. It may sound like I'm overreacting. After all, children bump their heads all the time. And in most cases, this results in nothing more than minor bumps, bruises or cuts in the scalp.

Is diet soda so bad that I should stop drinking it?

DEAR DOCTOR K: I love diet soda, but I've been hearing that it's not good for me. Is it so bad that I should stop drinking it?

DEAR READER: The introduction of sugar-free sodas (or "soft drinks") decades ago seemed like a blessing. Now you could enjoy the flavor, carbonation and caffeine of soda without the calories and weight gain. (Not to mention the diseases that go along with obesity, such as diabetes and heart disease.) What's not to like? I surely believed it: I've been drinking a diet soda nearly every day and avoiding sugary drinks for 30 years. But there are growing doubts about whether diet sodas really help people lose weight and avoid diabetes.

How can I protect myself and my family against Lyme disease?

DEAR DOCTOR K: A young pop singer who battled Lyme disease was recently on the cover of People magazine. I know it's silly, but if a celebrity can get a disease, I feel I'm more vulnerable. What should I do to protect myself and my family?

DEAR READER: Lyme disease is a serious illness that can have lasting effects. Fortunately, there are many things you can do to protect yourself. Lyme disease is an infection caused by bacteria that live inside insects (primarily deer ticks). When the ticks bite us, the bacteria enter our bodies. Deer ticks are very small, about the size of a poppy seed.

What can I do to make sex painless and pleasurable again?

DEAR DOCTOR K: I'm a man, and sex is often painful. Why? What can I do to make sex painless and pleasurable again?

DEAR READER: If you go by what you see on TV, the only thing standing between you and a satisfying sex life is erectile dysfunction. The truth is, pain during sex can also be an obstacle. I spoke to my colleague Dr. Michael O'Leary, a professor of surgery at Harvard-affiliated Brigham and Women's Hospital. He noted that while the reason for painful sex can be difficult to diagnose and treat, it's worth talking to your doctor. Together, you may be able to identify the problem -- and a solution.

Is it normal to have pain from whiplash months after a car accident?

DEAR DOCTOR K: I was in a car accident several months ago and got whiplash. I still have neck pain. Is this normal?

DEAR READER: The neck contains a stack of bones (vertebrae) with joints between them. The bones are attached to muscles and ligaments that hold them together, and that hold the neck upright, allowing it to move as your head moves. Whiplash -- the term used to describe a group of symptoms and also the typical accident that leads to them -- can damage one or more of these delicate structures. Whiplash is most commonly caused by car crashes, particularly those in which another car plows into the back of your car.

Do I need surgery to have my gallstones removed?

DEAR DOCTOR K: I was recently diagnosed with gallstones, and my doctor recommended surgery. Is this the best option, or can I consider other treatments?

DEAR READER: Gallstones are pebble-like deposits that form inside the gallbladder, a pouch that sits below the liver. It collects bile that has been made in the liver, then releases it into the small intestine through narrow tubes called bile ducts. Bile is a fluid that helps with digestion. It contains salts, cholesterol and bilirubin.

Is my birth control what’s causing me nausea and severe headaches?

DEAR DOCTOR K: I started taking combined birth control pills a few months ago. Ever since then, I sometimes feel nauseous and get severe headaches. Should I switch to a different pill?

DEAR READER: Nausea and headaches are common side effects of birth control pills, but they usually can be eliminated by adjusting the pills. Combined birth control pills contain the hormones estrogen and progestogen. When taken correctly, they are 98 percent to 99 percent effective in preventing pregnancy. But these hormones can cause side effects.

My wife had a mini-stroke. Can she have an angioplasty to open the narrowed brain artery?

DEAR DOCTOR K: My wife had a mini-stroke. The doctor said she has a narrowed artery in her brain. Can't the doctor open it up with angioplasty, as he would if she had a narrowed heart artery?

DEAR READER: "Mini-stroke" is another name for a transient ischemic attack, or TIA. A TIA causes stroke symptoms -- such as sudden weakness on one side of the body, blurred vision or difficulty speaking -- that last 10 minutes or more, but less than 24 hours. A TIA is a warning sign of an impending stroke. Four to 10 percent of people who have a TIA will go on to have a full-blown stroke.

How can I stop my son from sleepwalking?

DEAR DOCTOR K: My 8-year-old son has started sleepwalking. I'm worried he will hurt himself in his sleep. Is there anything I can do to stop him from sleepwalking?

DEAR READER: A person who is sleepwalking walks or makes other movements while being still largely asleep. A sleepwalker can be difficult to awaken fully and typically has no memory of the episode in the morning. I hope it will ease your worry to know that episodes of sleepwalking are usually brief and harmless.

What is Meniere’s disease, and what can be done to treat it?

DEAR DOCTOR K: I've been feeling dizzy and have had a constant ringing in my ears. My doctor has diagnosed me with Meniere's disease. What is this, and what can be done to treat it?

DEAR READER: In Meniere's disease, fluid collects in the inner ear. The inner ear is a complex system that is critical to both hearing and balance. Sound waves hit a membrane (the "eardrum") in the middle ear. The vibrations of the membrane are transmitted to tiny bones in the middle ear, and then to another membrane that starts the inner ear. Inside the inner ear is a snail-shaped structure called the cochlea. The cochlea transforms sound waves into nerve impulses that the brain can interpret. That's how we hear.