Some people have nightmares, others fear tall buildings and others cringe at the sound of airplanes overhead.
Many New Yorkers suffer the psychological impact of the September 11 attacks, some adopting quirky new habits, others enduring full-blown post-traumatic stress disorder, or PTSD, experts say.
"It's five years later, and it hasn't stopped, the nightmares, the shaking, the trauma," said Linda Gormley, who ran for her life as the planes hit the World Trade Centre and later developed PTSD.
"You just learn a new normal. You learn to live a different way," she said.
On September 11, 2001, Ms Gormley emerged from a commuter train as the first plane struck and was still running through flames, hot ash and shattered glass as the second plane hit. Minutes later, as she watched the south tower collapse, it seemed to be tipping directly towards her.
Now, hearing loud noises or screams can trigger panic attacks. If she sees someone running, she said she can't help but start running along with them.
"It's an automatic thing that I do. They might be running for the ferry, but I think they're running away from something, and something bad has happened," said the executive assistant.
Calls to the city's leading mental health referral line LifeNet averaged 3,000 a month before the attacks. Now they run at a monthly average of 8,000, officials say.
Calls peaked at 12,000 around the first anniversary of the attack, said LifeNet director Gillian Murphy.
"It's gone back down but never to pre-September 11 levels," she said. "People call and say either, 'It's the anniversary and I realise that I'm very very anxious,' or 'It's five years later and I never thought I needed any assistance but in looking back over the five years, I haven't really been doing very well.'"
"They're people who are just coming to terms with the fact they might need help," she said.
As many as 150,000 adults in the New York area were estimated to have suffered full-blown PTSD after the attacks. Probably an even greater number experienced partial symptoms, said Randall Marshall, director of Trauma Studies at the New York State Psychiatric Institute.
Most don't seek treatment. Their symptoms can include irritability, sleeplessness, anxiety, depression or loss of appetite, Dr Marshall said. "It's a continuum of reactions. It isn't as if you have it or you're fine."
For many New Yorkers, changes have been subtle.
"I've become more cautious. I stand close to the subway doors," said Tomoko Prokai, who works in sales. "It's a position where I can really look around."
Photographer Willie Way is always aware when airplanes fly overhead. "I'm always looking up all the time," he said. Pina Ascoly, who teaches Italian, no longer takes visitors to see the sights from the tops of tall buildings. "To tell you the truth, I'm a little bit afraid," she said. Retiree Veronica Beers said she grew angry after September 11. "I put on all of my buttons and started going to all the peace marches. I hadn't done that before," she said.
Not all the impact was negative. Terry Madison, a computer technician, said he is more patient and makes special effort to help tourists find their way.
"After September 11, I wanted people to think better of New York. It woke me up to just how much I love this city," Mr Madison said.
Reactions can be as varied as the people having them, said Edward Kantor, a professor at the University of Virginia who specialises in disaster psychiatry.
"What people need and how they recover and what makes them feel better and what makes them feel worse is very much an individual thing," he said.
"Vigilance is part of a normal response to danger," he added. "When it becomes pathological is when it keeps you from functioning in the rest of your life."