DEAR DR. ROACH: I need help with my mother’s question (she’s 86). She reports hearing glass breaking or being smashed. It’s so loud that it wakes her out of her sleep. She looks around and never is there a glass broken. She says it’s also a loud crashing noise, like something slamming up against a door. This only happens at night in her sleep. She states that it only happens a couple times a year for many years. I’ve told her it’s a dream or semidream state. She’s convinced that there is a specific medical name and explanation for her experience. Her name is Sarah. – N.D.

ANSWER: Sarah, you were right, this is a known condition, and it is called a hypnopompic hallucination. For some people, these hallucinations are visual; for others, they are auditory. They can occasionally be tactile. Your daughter is also right in that it is very like a dream state, except that it happens only as you wake up.

Often, it can be accompanied by sleep paralysis, an inability to move anything for a minute or two, which can be frightening. About 20% of the population can get this on a rare basis, but people with narcolepsy can get it very often. Since you are having them rarely, it is not something you need to worry about.

DEAR DR. ROACH: I have seen very little written about lactose intolerance. I am a 79-year-old woman in excellent health. Over the past year or two, I experience gas, loose bowel movements and occasionally explosive diarrhea. A colonoscopy and blood tests revealed no cause. A few months ago, I decided to monitor all dairy in my diet, and the symptoms have improved with the help of taking lactase tablets when I eat any dairy. I diligently read lists of ingredients and I’m surprised by all the foods which contain milk, such as bread. If I forget to take lactase, the symptoms reappear about 2 1/2 hours after eating the culprit food. Is there anything else I can take later at the onset of the symptoms to ward off the digestive distress? And is there any way to regain the missing intestinal enzyme that causes the problems to begin with? – J.A.T.

ANSWER: Lactose intolerance is caused by an inability to make the enzyme lactase, which breaks down lactose (a sugar found in milk). Without this enzyme, the sugar cannot be metabolized, and is digested by intestinal bacteria, creating hydrogen gas and short-chain fatty acids, which in turn cause symptoms. The “digestive distress” you delicately mention can include abdominal pain, gas, bloating and diarrhea.

Lactose intolerance is common, and people are more likely to develop it as they get older. The amount of lactose needed to cause symptoms varies greatly between one person and another, depending on the amount of lactase enzyme they make. Those with very little have the worst symptoms. It sounds like you have a very significant loss of the enzyme.

Treatment is to reduce lactose intake, and reading labels is certainly your best bet. People with milder disease can do fine just by eliminating milk and ice cream, which have the highest amount of lactose. The lactase enzyme replacement tablets, such as Lactaid, are effective for many and allow them to consume dairy products.

Once the lactose is in your system, you are out of luck if you haven’t taken the lactase enzyme. There’s no way to get the enzyme in ahead of the lactose load to your intestines. Sadly, gene therapy to replace the enzyme is not a reality.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or send mail to 628 Virginia Dr., Orlando, FL 32803.