DEAR ABBY: Six years ago, my husband and I went to the Netherlands to celebrate our 35th wedding anniversary. We had planned and saved for the trip for many years. Another married couple, our best friends, were going with us. My mother had had several operations for cancer, but her doctor said she could live another six months to a year.

You can probably guess what happened. We went off on this trip, and the second week of our holiday I got a call from my brother telling me that Mom was in the hospital, but he didn't think I should cut my trip short and come home. I did not go home, but my mother took a sudden turn for the worse and died the next day. We had taken a weekend side trip and missed the telephone message giving us the news, so I missed my mother's funeral.

A day has not gone by that I haven't wept bitter tears and asked God to forgive me. My mother had sacrificed so much for me, and I wasn't even there to pay my last respects.

Just writing this has helped, but I still feel guilty. Maybe this will help others. Have you any words of comfort for me? -- SORRY AND SAD

DEAR SORRY: This "serenity prayer" has helped many who have tormented themselves with recrimination about something they have or have not done. It's the prayer for Alcoholics Anonymous. I hope you will commit it to memory, and use it often:

God grant me the serenity to accept

the things I cannot change,

Courage to change the things I can,

and the wisdom to know the difference.

DEAR ABBY: When my dog "Robert" died, I received an unusual memorial from a friend. It was such a good idea, I want to pass it along. A donation was sent in Robert's memory to the Companion Animal Fund of the College of Veterinary Medicine, Iowa State University. The purpose of the fund is to support pet health research, and to purchase critically needed surgical and diagnostic equipment. Other colleges of veterinary medicine must have similar funds.

I also received memorials to the local humane society -- a good idea, too. -- ROBY KESLER, CEDAR RAPIDS, IOWA

DEAR ROBY KESLER: In a sense, donations of this kind return to pets some of the physical and emotional benefits they so generously bestow upon all of us. How rewarding to know that research in your pet's name will not only help to perpetuate his memory, but possibly lengthen the lives of other pets as well.

DEAR ABBY: I read your "chuckle for today" in which you mentioned my late husband, George Jessel. Thank you.

My "chuckle" for a lot of days: I once wrote a short column for a small monthly newsletter in San Jose, Calif. I mentioned to George that maybe one day I might be famous, too. His only comment: "Honey, your only claim to fame is that you are younger than Shirley Temple."

Honest. I did love him. -- MRS. GEORGE JESSEL, PACIFICA, CALIF.

Hot off the press -- Abby's new booklet, "The Anger in All of Us and How to Deal With It." To order, send a long, business-size, self-addressed envelope, plus check or money order for $3.95 ($4.50 in Canada) to: Dear Abby, Anger Booklet, P.O. Box 447, Mount Morris, Ill. 61054. (Postage is included.)

DEAR ABBY: Several years ago, you printed several letters concerning older people who had heard music inside their heads. I would appreciate any information you can give me, because my 92-year-old mother is experiencing those symptoms and needs reassurance that she is not "going crazy."

Thank you for your assistance in this matter, and for many years of unadulterated information and pleasure. -- JUDITH PHILLIPS, R.N., CANYON, TEXAS

DEAR JUDITH: That problem continues to surface from time to time, and when I explain that it is not unusual, readers are greatly relieved to learn that they are not alone. Here they are again:

DEAR ABBY: Thank you for printing those letters from people who keep hearing music in their heads. I am one. I am now 76, and never told others because I was afraid of what they might think. I have been a nurse for more than 50 years and had never heard of this condition. I feared that maybe I was getting senile. I was truly relieved after reading in your column that many others had the same experience.

During my waking hours, I hear hymns and waltzes. All the waltzes I loved to dance to keep drifting through my mind. Now I can tell my doctor about it and not be afraid that he will look at me and think, "Poor soul. She is really failing!" -- EMILIE IN BUCKS COUNTY

DEAR EMILIE: You would not believe the number of letters from readers who had also been hearing things and doubted their sanity. One man said he nearly went crazy because he heard bees buzzing continually in one ear -- night and day. Another said he heard constant crackling sounds, like bacon frying. A woman heard the "chirping" of crickets. Still another said it sounded like a freight train was roaring through her head. All feared they were going mad.

The sounds are due to a condition called "tinnitus," but the musical hallucinations are yet another matter. Read on:

DEAR ABBY: It was interesting seeing all the letters sent to you by people with musical hallucinations.

The two cases I describe in my book, "The Man Who Mistook His Wife for a Hat," were rather rare and special examples of musical epilepsy associated with damage to the brain. But musical hallucinations are relatively common, especially in older people, and though they should be checked out, nearly always turn out to be benign -- a nuisance, but not necessarily a sign of neurological disease. Readers should be assured about this. -- OLIVER SACKS, M.D., PROFESSOR OF NEUROLOGY, ALBERT EINSTEIN COLLEGE OF MEDICINE, BRONX, N.Y.

DEAR ABBY: I'm in my late 60s and profoundly deaf. I also have a severe case of tinnitus, which is a chronic ringing sensation in my ears. My case is unbelievable. The sounds might be compared to a bad LSD trip without psychedelic visions. They sometimes last as long as four days.

Like most people, you will probably think I'm a nut case. I hear music or singing, or both -- the same compositions over and over. Would you be good enough to consult one of your authorities to verify the fact that I am not crazy? I believe that would be an otorhinolaryngologist. This small town does not have such a specialist. Hoping you can help me ... HEARING THINGS

DEAR HEARING: Write to: The American Tinnitus Association, P.O. Box 5, Portland, Ore. 97207. You will be referred to a specialist near you. Please enclose a long, self-addressed stamped envelope (75 cents) and $1 to cover the cost of their printed materials. It's a pittance to pay for peace of mind.

This one's for everybody, from teens to seniors. To purchase Abby's new booklet, "The Anger in All of Us and How to Deal With It," send a long, business-size, self-addressed envelope, plus check or money order for $3.95 ($4.50 in Canada) to: Dear Abby, Anger Booklet, P.O. Box 447, Mount Morris, Ill. 61054. (Postage is included.)

DEAR ABBY: Several years ago, I read in your column about people having a problem with dry mouth.

I failed to keep the article in which you kindly offered information about my problem. Please print it again, and this time, I will make a note of the solution. I've read of other remedies, but I believe your information was the best. -- SPITTING COTTON

DEAR SPITTING COTTON: The column to which you referred was printed in October 1987, but here it is again:

DEAR ABBY: A while back you recommended a "saliva substitute" for people who suffer from dry mouth. Having suffered from that condition for two years, I went immediately to the pharmacy and asked for a saliva substitute. The pharmacist said she had never heard of such a product and told me to ask my dentist what the brand name was.

I called my dentist, and he had never heard of a saliva substitute either. Abby, can you tell me the name of this product and where it can be purchased? -- NEEDS IT IN ILLINOIS

DEAR NEEDS: I had no idea that the problem of "dry mouth" was so widespread until I mentioned it in my column and was promptly deluged with letters from readers seeking relief from that condition.

There are at least four brands of saliva substitutes on the market today. Ask your pharmacist to check the Annual Pharmacists' Reference Red Book, Facts and Comparisons, or Physicians' Desk Reference for Non-Prescription Drugs under "Saliva Substitutes."

Readers, for your information, "xerostomia" (dry mouth) can be caused by disease, medication, radiation therapy or the normal aging process. This condition can cause acute discomfort, tooth decay, inability to eat, swallow or talk, as well as difficulty in wearing dentures.

If your pharmacist has never heard of it and doesn't know where to get saliva substitutes, find another pharmacist.

DEAR ABBY: I am writing to thank you for an article that you ran recently that has given me more relief and comfort than I can describe.

I am 83, male and reasonably healthy, but in recent years I've been terribly troubled with a dry mouth -- especially at night. I complained to my doctor. He just shrugged his shoulders. Then I read your column in the San Francisco Chronicle, and my prayers were answered! In response to a letter asking why a person would use a mouth spray in public, you quoted a dentist who said that as a result of disease, medication, radiation therapy or simply aging, a number of people suffer from "xerostomia" (dry mouth).

I immediately phoned my druggist, and he had never heard of a saliva substitute, so I told him to call his supplier and order it.

He did, and the next day I picked it up and used it. Abby, I will be eternally grateful to you and that dentist. No more dry mouth! God bless you. -- GRATEFUL IN PARADISE, CALIF.

DEAR GRATEFUL: I'll print your letter for the benefit of others who suffer from dry mouth and are not aware of saliva substitutes.

Most teen-agers do not know the facts about drugs, AIDS, and how to prevent unwanted pregnancy. It's all in Abby's updated, expanded booklet, "What Every Teen Should Know." To order, send a business-size, self-addressed envelope, plus check or money order for $3.95 ($4.50 in Canada) to: Dear Abby, Teen Booklet, P.O. Box 447, Mount Morris, Ill. 61054. (Postage is included.)