'Twas the season for shopping, traveling, baking, wrapping, decorating, visiting and entertaining.

But the party's over.

'Tis the season now for post-holiday letdown, a phenomenon that mental health experts say occurs in early January and sometimes lasts through February, aggravated by the winter doldrums.

For some people, especially those who strung hundreds of lights, baked 20 dozen cookies, entertained two tables of guests, penned fourscore cards and wrapped armfuls of gifts, the new year brings blessed relief.

For others, the fading echo of New Year's noisemakers rings hollow: It's hard to get motivated, hard to concentrate, hard to care.

Discarded Christmas trees tossed into garbage bins signal an end to merrymaking -- and a jolting return to the status quo.

"I feel lost," says Mary Lane of Arlington, whose son, an Air Force pilot, and daughter-in-law returned to California last Tuesday after a two-week visit.

"They were here, and there was all this activity and now they're gone and we have to take down the Christmas tree," Lane says. "I get a real thrill out of having family and friends over. And then in January, everything comes to a halt."

David Herzog, a lawyer in Indianapolis, says he finds it hard these days to concentrate and get back to the same level of intensity he worked at in the weeks leading up to the end of the year.

Before the holidays, "I was swamped at work, but I got a lot accomplished," he says. "If you have something to anticipate, which I did, you don't mind doing the work."

But now that a holiday trip to New York is behind him, "all I have to anticipate for the next umpteen weeks is getting up in the morning and going to work," Herzog says. "I don't have a nice vacation right around the corner that gives me the drive and motivation to attack my job, rather than just do my job.

"Remember when you were in grade school?" Herzog asks. "Wasn't Friday a great day? Why was it? You're still in school. But compare Friday to Monday. You're doing the same thing. But Friday is much more fun because you have a whole weekend to look forward to."

Post-holiday letdown may seem to many a minor discomfort. But for some the malady hits hard.

"For a short period of time after the holidays we are significantly busier with patients in emergency psychiatric work," says Kenneth D. Isselkoen, director of emergency service and community education for the Northwest Center for Community Health in Reston.

Most people, he says, are depressed over unmet needs, dashed expectations and crises that occurred over the holidays.

Even for those who just feel melancholy, it can be an ordeal to overcome the blues because "it's a little depressing and often disappointing to accept that to change one's condition it's going to take time, energy and effort," says Joan Medway, director of the Women's Psychotherapy Center in Gaithersburg and clinical director of social work at the Psychiatric Institute of Montgomery County.

The first step, mental health experts say, is to acknowledge the symptoms of letdown -- a lack of energy and drive, a desire to hide and withdraw and an inability to sleep, eat and enjoy things that are usually pleasurable -- and to recognize their underlying causes.

"Sometimes there is so much commotion and fanfare leading up to the holidays that we expect them to be much more than they are," says Isselkoen.

"We expect the holidays to nourish us, cure our ills and revitalize and refresh us. But very often they're a disappointment and they don't live up to our expectations."

The converse is also true.

"The holiday season is lots of fun and it permits us and encourages us to regress," Medway says. "There's Santa Claus and gifts, getting things for nothing and the removal of rules. It's good that we regress that way. We took a breather, but now it's time to take hold and to function as an adult."

Warning: The reentry can be rocky.

"It's similar to what everybody experiences on a Monday morning going back to work after a pleasant weekend, only it's much more extreme," adds Dr. Alan Levenson, head of the department of psychiatry at the University of Arizona College of Medicine.

"It's a situation of going back to the routine and back to deadlines, requirements and responsibilities at work or at home that people were able to put off."

In late November and early December, Levenson says, "a lot of people were able to say: 'I'll deal with that after the holidays. Nobody's going to expect me to do that now. I'll take care of it the first of the year.'

"Well, the first of the year is here, and now is the time people face all those things that they put off."

Also contributing to the letdown is the sudden absence of the natural high -- the feeling of exhilaration that hits when people are in the midst of an intensely pleasurable activity.

"This is something that is experienced also with other types of events where you have a buildup," says Alix Rey, chief of psychiatry at Howard County General Hospital.

People who anticipate and attend the Mardi Gras and the Indianapolis 500 experience it.

The mother who spends months preparing for her daughter's wedding experiences it.

The loyal fans who follow the home team's bid for a sports championship experience it.

And "marathon runners preparing for a race experience it," says Rey. "You build up, build up and then the event happens and everything falls down."

For many, the period of holiday revelry is also a time of overindulgence. And the after-effect is sluggishness.

"The holidays are exhausting," says Medway. "People overfunction. They overwork, overspend, overeat, overdrink and overplay. And some of it really feels great. But afterward, you've got to deal with it."

Call it "stimulus overload," says Dr. Brian Doyle, clinical professor of psychiatry and family medicine at Georgetown University Medical School. "It's as if our bodies are telling us: 'Enough already. Get back to living sensibly.'"

The overfunctioning can also be emotional, Medway says, "especially if one is alone and is fighting off feelings of loneliness and of depression. That takes a lot of energy."

So does battling the winter blahs, which often worsen and extend the post-holiday letdown.

"We all tend to retreat to the hearth when it's cold and it's dark," says Doyle. "Long before the Christian focus on Christmas and the birth of Christ, there have been mid-winter celebrations by mankind relating to the rekindling of life and of hope.

"In other words, that it isn't all going to be endlessly black and cold. Spring will come. There's reason to be hopeful."

Nevertheless, a black cloud hangs over the prospect, and never more overwhelmingly than in the cold and dreary days of January and February.

Cabin fever, the stress that comes when people are cooped up in tight quarters without relief, can lead to irritability, short fuses and a sense of melancholy.

But for some people, the dark days of winter lead to a full-blown depression. These people suffer from Seasonal Affective Disorder, or SAD, a clinical disorder recognized by the American Psychiatric Association.

According to Dr. Norman Rosenthal, a SAD researcher at the National Institute of Mental Health, the disorder is believed to be caused by "some kind of vulnerability of brain chemical regulation, probably hereditary, which emerges when there's not enough light around."

Rosenthal estimates, based on a November telephone survey of 420 Montgomery County residents, that seasonal change is a problem in 25 percent of the population and a marked problem in 5 percent of the cases.

Dalene Barry of Washington is one of those with a marked problem.

"Every once in awhile I get overwhelmed with some kind of grief feeling," Barry says. "I'll just start crying and there is no reason for it. Or something happens, maybe with my children or with work, that totally shatters me.

"Or I'll overreact, either being sad or snappy. It's the kind of thing where if one of my children had done the same thing six months earlier or six months later, I would just pass it off."

To counter the symptoms of SAD, Barry undergoes light therapy in her home under the guidance of the NIMH.

"It gives an amazing boost," she says. "It's so strange and peculiar that lights can do that for you."

For most of us, however, our post-holiday feelings of melancholy or depression are not related to a mental or biological disorder. They're to be expected.

"This is a time when we naturally reassess our life's circumstances and hopes for the future," says Medway, "and there are some natural feelings that go along with that.

"Perhaps there's disappointment with present circumstances. Perhaps we're sad about some losses in health, financial status and personal relationships. And often we're impatient with wanting some very quick, magical solutions."

Sometimes, she adds, "it's very, very hard to remind ourselves that it take a lot of thought, focus, energy and time to pull out of the regression that is causing these feelings."