Robert Klitzman is a professor of psychiatry and director of the Masters of Bioethics Program at Columbia University. He is author of "The Ethics Police? The Struggle to Make Human Research Safe." The opinions expressed in this commentary are solely those of the author. View more opinion articles on CNN.

(CNN) "If this is what life is going to be like," my father said, "I don't want it."

I was astonished. To me, life seemed precious. It still does.

But two months earlier, he had developed leukemia and was undergoing aggressive chemotherapy. He was 78 and had survived the Great Depression, decades of hearing loss and open-heart surgery. My father was tough, but now felt unrelenting nausea, unrelieved by medication. He had lost weight and was now ash grey and weak. I had never seen him as distraught. Yet his doctors were still doing everything they could to keep him alive.

Sadly, his symptoms never disappeared. A month later, he died.

I have recently been reflecting on my father's death, in reading about David Goodall -- the 104-year-old Australian scientist who flew to Switzerland in May to have doctors end his life. Until recently, Goodall had worked at a university and enjoyed performing in a local theater. But with deteriorating health, he was no longer able to enjoy life as he once had. Given this reality, Goodall preferred to die. And he wanted his decision to promote the legalization of physician aid-in-dying (PAD) around the world.

Opponents of the practice tend to call it physician-assisted suicide, which carries a negative connotation for many. This term may suggest that these patients, with severe cancer like my father, simply want to give up, cannot cope and do not want to live. In fact, these patients want to live, but realize that they are facing death, and want to avoid unnecessary suffering and die with dignity. This being the case, proponents prefer the term physician assisted-death or physician aid-in-dying.

Still, physician aid-in-dying remains controversial. As a doctor, the idea that I should help patients end their lives makes me uncomfortable; my medical education inculcated the need always to help patients as much as possible. During my medical training, I treated several patients who said they just wanted to die. Yet they seemed depressed, distressed or, I sensed, didn't fully understand that we were trying to help them.

Many doctors have trouble addressing this issue, often finding it difficult to speak of death as part of life. We generally see death as failure, not part of an ongoing process or trajectory.

"I never like to use the 'F' word," a fellow physician recently told me.

"The 'F' word?"

"Futility." The term frightens both doctors and patients. It is often easier to continue to provide more treatment, even when zero hope remains.

But having witnessed my father's suffering close up -- how, when treatments become futile, disease can become too much -- I developed a different perspective. With my patients, I perceived these issues from my own position as a doctor. With my father, it was different. I knew how much he loved family, golf and the opera. I saw the situation from his point of view. Never before had I heard him question life's value.

Thanks to him, I came realize that, at a certain point, sadly, life may not be worth the immeasurable suffering of an unalterable disease.

This is not how much of America views life. While a number of states have debated whether to legalize physician aid-in-dying, in the US, it has been an option in only six states and the District of Columbia, and is generally limited to individuals with a terminal disease whom doctors expect to die within six months.

The American Medical Association opposes physician aid-in-dying, though, according to a 2016 Medscape poll, more than half of US physicians support it for terminally ill patients. Some disability advocates, though by no means all, fear a slippery slope : that if allowed, PAD would be inappropriately used against disabled patients.

But despite critics' fears, there is no evidence of this abuse in states such as Oregon and Washington , where the practice is legal. Care is taken to ensure that the patient is making a coherent and informed decision, and PAD has accounted for less than 1% of all deaths in these two states combined.

JUST WATCHED Gorsuch's views on assisted suicide under fire Replay More Videos ... MUST WATCH Gorsuch's views on assisted suicide under fire 04:57

A major hurdle in giving terminally ill patients the right to PAD appears to be our own difficulty confronting our mortality. I have seen comatose patients in their 90s, whose families want doctors to start invasive procedures when the patients will surely die in a few days or weeks.

Most people hope that they will never have to confront the reality of a terminal illness. But, alas, the odds are that many of us will find ourselves in this position, as David Goodall did.

His decision should encourage us to consider how we each would want to die -- if we would prefer physician aid-in-dying or the agony of aggressive, and ultimately ineffective treatment or other options. We should speak beforehand with our loved ones and doctors about these wishes. These conversations in advance are crucial, since when these medical decisions need to be made, patients frequently lack the cognitive abilities to make them. Yet, unfortunately, countless people fail to have such discussions.

Follow CNN Opinion Join us on Twitter and Facebook

Sadly, it took my father's suffering to teach me what medical school did not: At a certain point, the suffering of ongoing treatment does not constitute a life worth living. I hope other patients and families might consider these issues while they still can, and that policymakers and voters allow patients to have this option in carefully specified and monitored circumstances.

I hope, too, that if I ever have to confront this decision, I will be allowed to make a choice.