While the resilient are at peace with the idea of death long before a loved one dies, his research shows, the opposite is true of people who remain mired in grief: Death alarms them so deeply that they don't want to acknowledge it. They also score highest in terms of being overly dependent on their spouses.

"There's a sense that they depended on the person who died for too many things, and the widow or widower can't be the same person without them there," Bonanno said.

So deep is this prolonged grieving, variously called complicated bereavement, unresolved grief and delayed grief reaction, that an American Psychiatric Association panel this year floated the idea of including extended grief in the definition of major depression in its revised diagnostic manual, the DSM-V, to be published next spring. The panel has since reconsidered.

For Barbara Stewart, the beginning was horrendous. She was stunned when her husband of 31 years, Mark, died unexpectedly from a heart attack in their home in 2001.

"I didn't have his memorial service until a month after he died," said Stewart, 71, a longtime volunteer with the Widowed Persons Association. "The loss of my husband was so traumatic for me. I'd just sit and cry. I couldn't deal with it. I didn't want to.

"Every day, I'd go to the funeral home to make the arrangements, and every day, I'd have to leave."

Even so, she gradually emerged into a new life.

"I believe in today," she said.

The grieving typically experience overwhelming sadness, sleeplessness, loss of appetite, anger, guilt, loneliness and helplessness. They can feel hollow inside. They can be overly sensitive to noise, preoccupied, unable to concentrate.

With complicated grieving, those symptoms become so intrusive over a long period of time that people can hardly function.

"They think about the deceased spouse constantly," said psychologist Dr. Florina Yuger, Sutter Center for Psychiatry's training director. "They can't be present in their life. They can't stand to be by themselves. There's an extreme denial of death and a desperate loneliness, and they often want to die themselves."

Researchers know that the circumstances of death can add a difficult element to bereavement. Survivors of someone who fades slowly from life, from Parkinson's or Alzheimer's, for example, have time to mourn the loss of their loved one for months or years before the actual death. The suddenness of traumatic death, on the other hand, can bring greater emotional suffering to survivors.

And a survivor's own emotional history, including past bouts with depression and post-traumatic stress disorder, can cause normal grief to lapse into a long bout of complicated grief, Yuger said.

"These things from the past get triggered," she said. "This can go on for years. The brain replays the death over and over again. It's hard for the brain to process the information and move forward."

Behavior therapy can help people suffering from complicated bereavement, she said; so can antidepressants.

"We want widows to learn healthy coping skills and confront painful situations without avoiding the trauma," Yuger said. "Avoidance makes the symptoms worse."

Almost 11 million: Americans age 65 and older who have lost their spouses, according to census data.