Susan had not eaten for weeks by the time she entered the hospice facility. A 75-year-old editor, she was dying from a brain tumor. As her body weakened, she grew confused and nearly comatose.

But suddenly, a few days later, she perked up and asked her brother for a liverwurst sandwich with sweet pickles. Relatives fetched the sandwich and she nibbled a few bites. More animated than in previous days, she engaged in lucid conversation. Soon thereafter, she slipped back into her comatose state and died two days later.

In speaking with the medical team, her brother learned that the brief rebound his sister experienced is called an “end-of-life rally.” Palliative care experts say revivals are common, although no one knows exactly why.

Doctor’s report that often patients would ask for a particular food associated with childhood or comfort. And, the request is generally explicit, say, a Diet Sprite rather than any old beverage.

“There’s great mystery around this,” said John Mastrojohn, the executive vice president of the National Hospice and Palliative Care Organization. “But everyone who works in the sector has a story.”

Anecdotally, doctors and nurses interviewed for this article said that a striking number of their dying patients had experienced a rally, also known as terminal lucidity. Bounce-backs generally last only a couple hours, but some go on for so long that the patients can take a break from a hospice for a few months.

Dr. Craig Blinderman, the director of adult palliative medicine at the Columbia University Medical Center, hears lots of stories. Yet evidence-based data is elusive, if nonexistent, he said. He postulated that as organs shut down, they can release a steroid like compound that briefly rouses the body. In the specific case of brain tumors, swelling occurs in the confined space of the skull. The edema shrinks as dying patients are weaned off food and drink, waking up the brain a bit.

These windows of energy can startle family members sitting at the bedside. Those who hold out hope that their loved ones may somehow recover may see the comebacks as encouraging. Some find the little flickers disturbing or even heartbreaking.

“I always provide a lot of anticipatory guidance, that you should not be surprised or alarmed or that it means that your loved one is healing,” Dr. Blinderman said. “Obviously you don’t want to dash hopes, but you have to make clear that Dad is not rising up from the dead like Jesus Christ.”

Physiologically, experts believe that the mind becomes more responsive when a dying patient is taken off the extensive fluids and medications such as chemotherapy that have toxic effects. Stopping the overload restores the body to more of its natural balance, and the dying briefly become more like their old selves.

Then there’s a spiritual or psychological component, which defies scientific explanation. Hospice professionals note a compelling desire to say goodbye or bond with loved ones in those last moments. There’s no way to test this hypothesis, but there’s no way to falsify it, either.

“People know when they are dying. They have this internal gut feeling that tends to expand at the end of life, and they seek a strong final connection,” said Dr. Blinderman.

These rallies frequently revolve around a relationship, particularly if the patient is waiting for a child to come from out of town to pay last respects.

I knew of a son who could not get home for a month. His mother was dying. The woman was mainly comatose during that time. He finally made it home. She responded, and then passed 15 minutes later.

Whatever the cause or source of these near death “awakenings” or hanging on for an event I am comforted to know there may be one more opportunity to say I love you.