Prof Robert Klitzman, of the Columbia University Centre for Bioethics and College of Physicians and Surgeons, said he would "never forget" the moment he heard about the planes hitting the World Trade Centre, where his sister worked on the 105th floor.
"That morning at 8.45am ... my mother called me and said, 'did you hear a plane hit that building where Karen works?''
After her memorial service, he said his "body gave out".
"I didn't want to get out of bed, I didn't feel like watching TV, listening to music."
However, despite being trained as a psychiatrist, he did not accept advice that he was suffering from depression, instead believing he had the flu.
"I was surprised that I didn't realise [I had depression]."
His experience on the other side of the doctor-patient relationship inspired him to write the book When Doctors Become Patients, for which he interviewed more than 70 medical professionals who had also been patients.
The experiences of these and other medical professionals could help "doctors be better doctors" and the book was used in medical schools for this purpose, he said.
An example was a man who had been a surgeon for 40 years and was told the night before undergoing surgery himself there was a 5% chance he would die.
He had a sleepless night before the surgery, but it was not until later that he realised he would have felt much better had the surgeon told him there was a 95% chance of success.
Prof Klitzman, who is visiting Dunedin as part of Genetics Otago's public lecture series, presented a talk on the subject with the University of Otago's Prof Mark Henaghan at the Dunedin Public Art Gallery this week.
During his trip to New Zealand, he has also lectured on the ethics associated with genetic testing, including on unborn children.
He said it could soon be possible for parents to choose whether they wanted a child based on attributes like whether it would be homosexual, or even what hair colour it would have.
It was also important to acknowledge the positives, as genetic testing could screen for many conditions, he said.
He will give a talk, called Am I My Genes?: Confronting fate and family secrets in the age of genetic testing, at the Edgewater Resort, in Wanaka, at 6pm tomorrow.
