Few people know what to expect as the end nears. But death, just like life, is a process, scientists say.
If a person has a long-term illness, it's common for the person to withdraw socially in the months before death. This means that the person may be less interested in certain activities, such as work or social gatherings.
"Often, [dying] people are very focused on their family and on things that are important to them to do before they die," said Dr. Nina O'Connor, director of palliative care at the University of Pennsylvania Health System.
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Moreover, people tend to have less energy toward the end of their lives. This fatigue prompts them to sleep more, often for most of the day. There are multiple causes for this fatigue. If the person has cancer, the cancer cells can consume a lot of the person's energy, O'Connor said. Also, irregular breathing can cause a person to have lower levels of oxygen and higher levels of carbon monoxide in their blood, which can lead to fatigue.
In addition, the person is likely eating and drinking less, which means they aren't getting enough calories to be active, O'Connor said. Dehydration can also lead to fatigue, Dr. Michele Casey, the regional medical director at Duke Health in North Carolina, previously told Live Science.
A person's appetite might dip for various reasons. Their body might be producing more catecholamine, a chemical in the blood that suppresses appetite. Increased catecholamine is common among people toward the end of life, especially in those with cancer, O'Connor said.
What's more, people might eat less because their intestines aren't working as well, meaning they have trouble processing the food they eat. "It might sit in their stomach or make them feel nauseous," O'Connor told Live Science. Furthermore, taste and smell are usually the first senses to go, so food and drink might not taste as good as they used to, she said.
People with advanced Alzheimer's disease often have physical difficulty swallowing, and they may forget how to chew and swallow. "Sometimes, they aren't physically able to eat," O'Connor said.
It can be upsetting for friends and family when a dying person eats less. "In our culture, we take care of people we love by feeding them," O'Connor said. "When people are sick, we make them soup and we push Gatorade."
However, loss of appetite and weight loss are natural parts of dying from many long-term illnesses, she said.
Diminished energy can cause a person to slow down. For example, they may move, talk and think more slowly than usual, and they may also need more time to process conversations, she said. Medications the person is taking, such as certain painkillers, may also slow them down, as can having out-of-balance electrolytes, O'Connor added.
"The physical fatigue and weakness [of people near the end] is profound," O'Connor said. "Simple things, like getting up out of bed and into a chair could be exhausting — that could be all of someone's energy for a day."
Because they have less energy, the person's body may have difficulty regulating temperature, meaning that they may be hotter or colder than usual, she said. [Why We Get Cranky When It's Hot Out]
In the last days or hours before death, people's breathing can become unusually shallow or deep. It can also be irregular, with pauses lasting from seconds to a minute or two, and that "can be scary for their family members who are watching," O'Connor said. "[But] all of it comes from the process of the body slowing and shutting down."
This change in breathing, however, doesn't appear to make the person uncomfortable, O'Connor said.
At the end, some people have a so-called "death rattle" when breathing. This happens because the person is unable to cough up or swallow secretions that build up in the chest and throat. This rattle doesn't appear to bother the patient, but it can be upsetting for loved ones to hear. To get rid of the rattle, it may help to change the patient's position, suction out the secretions, or give medications that get rid of the secretions, O'Connor said.
Despite moving slowly, hearing is one of the last senses to go. "As people are drifting in and out of consciousness, we know they can hear voices, especially familiar voices," O'Connor said. "We give loved ones the advice to keep talking, even if it seems like the person is sleeping."
When a person dies, physicians usually check for cardiac death (when the heart stops beating) or brain death (when there is no more electrical activity in the brain), O'Connor said.
If someone is a "vegetable," that means there is no more brain activity, and that life support is keeping the organs functioning. At that point, "legally, the life support is turned off because they have died," O'Connor said.
These two types of death — cardiac and brain — are used no matter how the person died. "It could be a sudden cardiac arrest, when the heart stops. It could be a bad trauma, when someone has a lot of bleeding and then their heart stops because there isn't enough blood flow," O'Connor said. "Or, you could have a bad neurologic injury and then have a brain death, where your brain doesn't have electrical activity, and then your body would follow."
However, there is anecdotal evidence that people whose hearts have stopped but are then restarted are able to describe accurate, verified accounts of what was happening around them, Dr. Sam Parnia, director of critical care and resuscitation research at NYU Langone School of Medicine in New York City, previously told Live Science.
"They'll describe watching doctors and nurses working; they'll describe having awareness of full conversations, of visual things that were going on, that would otherwise not be known to them," Parnia said. These accounts have been confirmed by medical staff who were in the same room, he noted.
For additional information on the dying process, O'Connor recommended two online resources: the website Get Palliative Care provides palliative care information, and the Hospice Foundation of America has resources on death, dying and grief.
Originally published on Live Science. Additional reporting by Elizabeth Palermo.
Editor's Note: This article was originally published on Jan. 29, 2014, and was updated on Dec. 8, 2017.
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Laura is the archaeology and Life's Little Mysteries editor at Live Science. She also reports on general science, including paleontology. Her work has appeared in The New York Times, Scholastic, Popular Science and Spectrum, a site on autism research. She has won multiple awards from the Society of Professional Journalists and the Washington Newspaper Publishers Association for her reporting at a weekly newspaper near Seattle. Laura holds a bachelor's degree in English literature and psychology from Washington University in St. Louis and a master's degree in science writing from NYU.