Dr. Najma Ahmed was getting ready for bed on Sunday evening when a text message lit up her phone.

She wouldn't really sleep for another three days.

Ahmed, the acting medical director at St. Michael's Hospital, was quickly thrust into the aftermath of one of the worst mass shootings Toronto has ever seen.

Five patients who were wounded in Faisal Hussain's deadly rampage on the Danforth were rushed to St. Michael's that night, including three who underwent "immediate life-saving surgery."

In the coming hours, Ahmed would operate on all three. Much of the focus has been on the victims who lost their lives, and rightfully so, she says — but those who survived the shooting will endure months of painful rehabilitation, too.

"It changes your life, and you're never the same," she told CBC News from an operating room at the hospital, a place she calls "a home."

Toronto is a city with heart and soul, as we've demonstrated. Its citizens rise whenever there is a challenge. - Dr. Najma Ahmed

At the outset, details about the incident were hazy. Police say the crack of bullets started echoing in Greektown at around 10 p.m.

Ahmed was the hospital's on-call backup surgeon at the time. All she knew was this was a "code orange" — some sort of mass casualty event.

Julianna Kozis, left, and Reese Fallon, right, were killed in the deadly rampage in Toronto's Greektown Sunday night. (Toronto Police Service/Facebook)

But as she neared the hospital and saw the lines of police cars and ambulances, it quickly became clear that this was something bigger than the usual car crash or stabbing.

"I had the sense it was going to be a tough night, and something catastrophic had happened in the city," she said.

Injuries pile up

It had. The 29-year-old shooter had wandered down the Danforth, indiscriminately firing. Witnesses described sheer chaos, as bloodied victims ran for their lives.

Reese Fallon, 18, and Julianna Kozis, 10, were both killed. Thirteen others were hurt.

Dr. Najma Ahmed, left, and Dr. Bernard Lawless, right, were both working at St. Michael's in the wake of Sunday's mass shooting on the Danforth. (Albert Leung/CBC)

A police source told CBC News that Hussain killed himself following an exchange of gunfire with officers.

In the aftermath, Sunnybrook and Michael Garron Hospital were similarly swamped with patients. Dr. Dan Cass, Sunnybrook's executive vice president and chief medical executive, said there was a scramble to clear the emergency room and make space for new patients.

But Ahmed didn't understand the sheer scope of what had happened when she arrived at the hospital. She just immediately started triaging patients.

The Greektown shooting late on July 22 took the lives of two people and injured 13 others. 0:59

While tending to the wounded on stretchers, she realized one person needed emergency surgery, and rushed him into the operating room.

It wasn't until 4 a.m. on Monday that she fully understood the entire city was in mourning.

The mood at the hospital that night was incredibly serious, she said. Everyone was on the same sort of unspoken wavelength — pull together and save as many lives as possible.

"Every single person I saw that night, I saw that in their eyes," she said.

'It's kind of soul crushing'

St. Michael's is no stranger to trauma patients. The hospital routinely sees people involved in shootings, stabbings, and catastrophic car wrecks.

But this incident was different, Ahmed said.

"Because it was in the heart of the city, and the loss of life was so tragic … it's kind of soul crushing."

Faisal Hussain captured on video walking past the Burger Stomper restaurant on the night of the deadly mass shooting. 0:34

Hussain's motives are still largely unclear. ISIS used an online post on Wednesday to claim responsibility for Sunday's attack, but police say they have "no evidence" to corroborate that link. ISIS did not provide any evidence to support its claim.

It's not lost on Ahmed that she is a doctor who happens to be Muslim, treating victims of an attack that has sparked much anti-Muslim rhetoric.

You know the <a href="https://twitter.com/hashtag/TorontoShooting?src=hash&ref_src=twsrc%5Etfw">#TorontoShooting</a> suspect? He was Muslim. You know who else was? <br><br>The head of the trauma unit that performed life saving surgery on five victims, and the cafe worker who cradled a victim in his arms as shots rang out.<br><br>Goodness is everywhere. —@MuhammadLila

Though she appreciates people commending her work, she's downplaying her importance.

"Lots of people on Earth, regardless of their faith or their religion — or even if they don't have faith in a god — get up every day and go about their business and try to make the world a better place. I'm just one of those billions of people. I just happen to be in the business of saving lives."

Shooting survivor Danielle Kane was treated by Ahmed. Family spokesperson Byron Abalos told CBC News that Ahmed saved Kane's life.

"I know that she is a Muslim woman and I know that there is sometimes backlash against the Muslim community because of the shooter, and I think it's important personally that we all recognize that one person does not represent the entire community," Abalos said.

In spite of Sunday's tragedy, Ahmed is convinced that the city's spirit will endure.

"Toronto is a city with heart and soul, as we've demonstrated. Its citizens rise whenever there is a challenge."

Watch the full interview here:

Dr. Najma Ahmed, who operated on and helped save the lives of several victims of the Sunday night shooting in Toronto, says a night like that 'changes your life, and you're never the same.' 6:08

adam.carter@cbc.ca