You feel a sudden pain. Perhaps you're frightened. Perhaps it's the middle of the night.

You wonder, "Should I call the doctor?" Or even go to a hospital emergency room?

Somehow you feel shy about "bothering" a doctor. Though this can be true any time of day, it is especially so in the middle of the night. Or the weekend.

You also know you'll feel dumb if it turns out to be "nothing."

One of the hardest medical questions for most of us is, "Shall I call the doctor? Must I call or do something now?"

Years ago, my wife and I used a pediatrician who invariably phoned us back when we called. Yet a few parents, talking about the same doctor, said, "It's hard to get him to call back."

I asked him about this, and he said, "I know that when you call, it may be something important."

Obviously, some parents called him too often about trivialities -- every twinge or sniffle. Drs. Donald Vickery and James Fries write: "The patient who frequently complains of severe pain from minor causes is in much the same situation as the boy who cried 'wolf'; calls for help will inevitably be taken less and less seriously by the doctor. This situation is a dangerous one, for the patient may have more difficulty in obtaining help when it is most needed." ::

When should you waste no time in calling -- or getting to an emergency room?

It is impossible in a brief article to list the many situations in which you should either see a doctor immediately or phone for advice or rush to an emergency department.

For the most complete guidance possible, I'd recommend one or more of the books discussed in this space last week: Vickery's and Fries' "Take Care of Yourself: The Consumer's Guide to Medical Care" (Addison-Wesley, $14.95); "Taking Care of Your Child: a Parents' Guide to Medical Care," by Drs. Robert Pantell, Vickery and Fries, (Addison-Wesley, $12.95). Or the "American Medical Association Family Medical Guide" (Random House, $29.95) or three smaller AMA guides, "The American Medical Association MEN {or WOMEN or CHILDREN}: How to Understand Your {or Their} Symptoms," (Random House, $9.95 each).

All these use simple flow charts to help you decide whether to get or phone for help immediately or take some lesser course. ::

There are some situations, however, where common sense ought to tell us: Do something.

The following "emergency signs" or conditions, say Vickery and Fries, "dictate that medical help be sought immediately": Major injuries like broken legs or major chest wounds. Vigorous bleeding that can't be stopped (usually it can) by applying pressure to the wound. Unconsciousness. Stupor -- decreased mental activity, short of unconsciousness -- or drowsiness. Ask a few questions: if someone isn't awake enough to answer questions about what has been happening, "urgent action is necessary." Disorientation. Someone who has been alert, then becomes confused and disoriented, someone who can't tell where they are, who they are or what day it is, should get prompt medical attention. Shortness of breath or difficulty in breathing, even though resting. (In young adults, this sometimes may be caused by hyperventilation -- that is, overbreathing, short breath and possibly chest pain, numbness, tingling sensations, dizziness or panic -- brought on by anxiety or nervousness. In younger adults, this is not usually serious. Still, if the condition is caused by severe pain -- or you're concerned or in doubt -- seek immediate attention.) Cold sweats -- not the usual sweating in response to heat or stress or medication like aspirin -- in someone complaining of chest or abdominal pain or a light-headed feeling. Severe pain. Another doctor adds: "Include chest pain -- everyone worries about a heart attack." Vickery and Fries say "see a physician now" if there is chest pain associated with shortness of breath, irregular pulse, sweating or dizziness or the pain is severe. Often, they add, a feeling of pressure or squeezing is more prominent than pain in a heart attack.

Kurt Butler and Dr. Lynn Rayner (in "The Best Medicine: The Complete Health and Preventive Medicine Handbook," (Harper & Row, 1985), add a few more conditions for which they believe medical care is needed right away. Among them: Severe burns, especially on the hands or face. Physiologic shock. Medically, "shock" is a term meaning "a serious disturbance of blood circulation that can follow injury, hemorrhage, poisoning, adverse drug reaction, heart attack and other conditions," Butler and Rayner explain. "The skin is pale, the pulse and breathing are rapid and weak, blood pressure is very low, thirst may be extreme." And "the patient should be kept warm and lying down with the head slightly lower than the body, and driven to a hospital." Knocked out teeth. If an adult's or a child's permanent tooth is broken or knocked out, the patient and the tooth (gently rinsed, but not rubbed, and immersed in milk) should be taken to a dentist immediately.

If a finger, hand, foot or any other body part is severed, put it in a clean, moistened towel, then in a plastic bag, then in a container with ice at the bottom to keep it cool, and rush it and the patient to the nearest hospital emergency room. It can often be reattached. ::

Butler and Rayner also include choking, since choking on food or something else can quickly cut off breathing and cause death.

"If medical personnel are more than a minute or so away," they say, apply the Heimlich maneuver. "Stand behind the person and bring your hands together at the base of the sternum {the breastbone} . . . Give a sharp thrust in and up . . . to force air out of the lungs {to} propel the object out of the windpipe. Someone else there should try to contact a physician" (I'd say phone 911) in case the object won't come out.

"If an infant or small child is choking, place it across your lap with head and arms hanging down. Using the heel of your hand, give several thumps between the shoulder blades."

Vickery and Fries more cautiously say: "We have not attempted to teach complex first-aid procedures such as cardiopulmonary resuscitation (CPR) or the abdominal-thrust (Heimlich) maneuver. To use these procedures correctly, you need intensive instruction and an opportunity to practice." Call your nearest hospital, American Red Cross or American Heart Association chapter about training. ::

In crises like the ones listed, Vickery and Fries advise, "Go to {a hospital} emergency room if it is close." If not, "you can often obtain help over the phone by calling an emergency room or the rescue squad . . . especially important if you think someone has swallowed poison."

Butler and Rayner say, "Generally speaking," call your doctor, if you have one. If you have to make a decision without the doctor or the situation is obviously urgent, "a car is usually the fastest way to get a patient to a doctor but should not be used if movement might cause further harm . . . An ambulance should be called when there is a severe back or neck injury or compound fracture (with a bone protruding from the skin) . . . {or} if resuscitation, say from drowning or smoke inhalation is required."

When in doubt, call 911. But don't use 911 as a taxi service. Someone in real need may suffer.Next Week: Doctors who get sick.