Awakened once again after midnight by music blaring from the apartment upstairs, a District magazine editor lies in his bed, eyes open. He fantasizes about making an elaborate contraption resembling a 12-foot hand drill to bore through the ceiling and into the bottom of the offending stereo. Kaboom! It explodes. The image repeats itself over and over.

A retired accountant, fearful to tend her garden near the tall fence separating her tomatoes from a neighbor's Rotweiller, sits on a nearby patio chair ashamed that she could even think the unthinkable -- lobbing a Mickey Finn T-bone over the fence. "I could never do such a thing. Never," says the mortified grandmother. "But it does keep coming to mind."

During his commutes home, after late hours at the office, confided the lawyer to his therapist, the idea of steering his car into the headlights of oncoming traffic has occurred to him. Often. Now this mini-drama of a loitering mind haunted and depressed him. How could a responsible husband and a loving father such as himself entertain such a bizarre notion so frequently?

"That steering into the opposite lane one is probably relatively common," says Eric Klinger, a professor of psychology at the University of Minnesota who admits the notion also has crossed his mind. Though seemingly suicidal and destructive, thoughts of accelerating into a tree, into an abutment, or off a bridge, are the pulp fantasies behind the wheel, he explains. And they're all characteristic of the gremlins of consciousness he labels "obsessional daydreaming."

The black sheep of common daydreaming, these fitful flights of fancy "run a range of brutal responses and brutal misadventures" and occur to "substantial percentages of people," says the author of "Daydreaming" (Tarcher, $18.95), a book that combines his findings of three decades of research into mental dalliance. Typically off-key and violent, sometimes frightening or disturbing, almost always contrary to the daydreamer's own mores and values, they are figments of imagination that blip onto the mental screen like a teaser for a chain saw massacre flick.

"It is what the analysts call 'ego alien.' They seem to come from outside of what you'd like to do and how you'd like to think of yourself," says Klinger.

To make matters worse, they tend to repeat themselves. But the good news, says Klinger, is that no matter how often such wicked whimsy occurs -- whether throwing a crying baby out the window or garroting the office bore -- people seldom act on it.

"In and of itself, it is probably not going to go anywhere," says Klinger. "It is a signal, an indication of something else going on in your life. That may be a matter of concern, but the fact that you are having a thought needn't be."

Klinger encourages people to view daydreams as tools of self-understanding, even if they seem like the musings of Walter Mitty's evil twin.In that respect, daydreaming has come a long way from the days when it was considered a sure sign of laziness and a classroom nuisance. So has the scientific study of daydreams, which were once seen only in strict Freudian terms as regressive activity, infantile and neurotic, a defense mechanism against the pressures and anxieties of everyday life.

Increasingly, scientists such as Klinger who have taken this subject into the laboratory, have come out daydream believers. Their research attributes to these spontaneous and short bursts of invention such functions as easing boredom, acting as mental bulletin boards, triggering creativity, boosting sexual pleasure, stimulating emotions and, generally, flagging unconscious agenda. But wandering minds want to know: What do the negative daydreams mean? The bloody ones? The lurid ones?

Klinger warns against trying to translate them too literally -- a mistake that obviously can be very upsetting. He recounts the story of one therapy patient who was tormented by his obsessional daydream: As he walked down the street, he imagined himself choking the women he saw and grabbing at the men's genitals. "I'd have these thoughts, probably hundreds of times a day," the patient reported. "These thoughts sometimes terrified me. I was afraid I'd do it. Yet I knew I didn't want to ... "

If the meaning of such episodes can be "quite different than what they seem," that doesn't absolve them of any important meaning at all, says Klinger. To imagine momentarily cutting your mother-in-law's throat isn't necessarily conspiracy to murder, he says, but it should raise some questions about the relationship. The notion of dropping your newborn doesn't mean you wish the baby harm, but it might invite some introspection about how you see yourself as a parent. The woman-strangling patient neither hated the opposite sex, nor did he want to sexually attack men -- but he did discover through therapy that his emotions toward both sexes had been blocked and stymied.

"I try to put these obsessive daydreams into a broader context," says Klinger, emphasizing that daydreaming has not been thoroughly researched and some conclusions are speculative.

"Daydreams seem to be triggered by things that remind of us what we want or what we fear, which then plays through our head components of that thing ... But it is necessary to say that no one interpretation is going to be valid for everybody."

Consider the highway daydream. One explanation, says Klinger, is that the person, at some level, is worried about head-on collisions, "particularly if the traffic is hairy, or you are tired. So that could easily trigger the daydream -- because it is what we fear and not because it is what we want."It also could result from stress in another part of the person's life that shows up when on the road again, he says. "If you are anxious about something else, anxiety tends to spill over and sensitize us to react to cues of other things that we fear."

A Freudian might well interpret the head-on daydream as an expression of a death wish. "Or, perhaps suicide is an option and you are aware of it and you are afraid of it," says Klinger. "You could also interpret it ... as a fear of losing control" not just of your car, but of your life.

In most cases, says Klinger, people needn't worry that these miniature 'day-mares' indicate that they're prone to self-destruction or violence. "If it scares them that much to have the thought, then that's a very good indication that, on the balance, they're not suicidal," he says. "On the other hand, somebody who is particularly ambivalent, who is closer to being suicidal, might also have some thoughts like that. So we can't simply exclude it either."

Typically, the reaction is the troublemaker rather than the obsessive thought itself. Cases in which someone regularly imagines germs on a doorknob can lead to washing and rewashing his hands, the kind of extreme obsessive-compulsive behavior described in the 1989 bestseller "The Boy Who Couldn't Stop Washing." While many people apparently daydream obsessively about raping or being raped, says Klinger, most of them don't act on it, nor do they want to. "The person needs to distinguish between the frequency of the obsessive thought and the realistic probability," he says.

On the other extreme are mischievous obsessional daydreams that tend to be more amusing than disturbing. "Very typical is when you are talking to somebody and, you are ready to pull away from the conversation but can't," says Klinger, "and you begin to have images of wringing that person's neck. That is a perfectly ordinary thought. It doesn't take much interpretation. But, if you don't recognize this, you should think about why you're unable to say you've got to go."

Because obsessional daydreams are the freaky sideshows outside the psychological big tent, Klinger recommends this kind of examination of the possible explanations.

"Fear is a very common instigator and probably, in one way or another, plays a role in all of them," he says. "But any flash like that which you get at all is an indication of something going on. Of course, the ideal would be to understand that from the beginning, from the very first one. You've had this thought and you think to yourself, 'Well, what am I saying to myself here? What am I signaling?' Once you recognize it, and realize that you aren't about to act on it, that can be reassuring ... But if you can in no way relate to it, and it is deeply troubling, that would suggest that you need to confront it."

Sometimes, says Klinger, that can be accomplished on one's own; other times, it requires outside help. He recalls one patient, a middle-aged professional whose obsessional daydreams involved self-mutilation. He thought he was going insane. Through psychotherapy, the patient discovered that his fantasies of injuring himself occurred usually after suffering disappointments with women.

"That he was horrified by the images suggested he didn't mean to hurt himself," says Klinger. But the self-mutilation came to signify his frustration over rejection. As he gradually accepted them as "communication" to himself, the daydreams subsided.

"Not everybody can drop everything and go off to a therapist," says Klinger. "And there is the fact that a substantial number of therapists aren't qualified to deal with such a question ... But, at the point that it becomes distressing, when it gets in the way, or where there are other problems in your life that may have some bearing on this, that warrants going to see a professional."

Generally speaking, he adds, obsessional daydreams are an indication there is something about yourself you don't understand. "You should try to find out ... No matter how negative, it is still an asset if you take it as information about yourself."