The patient was a 51-year-old man with no history of mental illness. He had a steady job and a solid marriage of 20 years. But in the weeks after the Sept. 11 attacks, he grew increasingly paranoid, thinking that his remote rural town was the next target.

He started climbing trees with binoculars to look out for suspicious characters. He thought the trucking firm he worked for was secretly transporting explosives. After he landed in the psych ward, he was happy not just to get treatment but because he “felt the hospital was relatively safe,” according to a case study published in the Southern Medical Journal.

The patient was suffering from what his doctors called “persistent paranoia,” and their report, published several years ago, serves as a reminder that in the days, weeks and even months after the Sept. 11, 2001, attacks, anyone could fall into the grip of fear, sometimes rational, sometimes not. We kept watch and planned evacuation routes. We stocked up on water and gas masks and sealed off our windows. The Jersey barriers went up and stayed up, becoming a permanent part of the landscape.

Now on the 10th anniversary of the attacks, the wounds have mostly healed with the balm of time and the catharsis of national remembrance. But there is still evidence of the psychological aftershocks: Within some of us, there is still a man in a tree with binoculars who is scanning the horizon.

And on Thursday night, a new potential danger was reported: The Associated Press said officials had received a “credible but unconfirmed terror threat” involving New York or Washington. The information was received late Wednesday, the AP said, but further details were not available.

According to a new Washington Post poll, almost half of Washington area residents say the Sept. 11 attacks caused a lasting change in their lives, including 14 percent who say it changed their day-to-day lives.

In 2004, 23 percent of Washingtonians said they avoided attending a public event out of fear of another attack. In the new poll, the figure dropped some, to 17 percent. But in a region with about 5.5 million residents, that’s a lot of people shying away from such events as concerts at Wolf Trap, July 4th fireworks on the Mall or Nationals games.

The poll of 1,010 randomly selected adults in the Washington area was conducted between July 29 and Aug. 29; it has a margin of error of 3.5 percentage points.

The survey found that more than one in five African Americans and lifelong District residents report avoiding an event, while fewer whites and Virginia and Maryland suburbanites say the same. Skipping an event is twice as common among those who think about the attacks “a lot,” compared with those who think about it less often.

For some, the Metro is not a convenient way to travel; it is a bull’s-eye.

So is the Mall. At least Beverly Josiah thinks so. She has tried to steer clear of it since Sept. 11, when she went there looking for her younger sister, who worked in a federal government office nearby.

“I was panicking,” she recalled. “There were police officers with their guns out and planes flying overhead. It was terrifying.”

For years, she had put the annual Cherry Blossom parade on her things-to-do list in Washington. “I took that off the list,” said Josiah, who is 41 and lives in Dale City. “Before, I never had a problem being in crowds.”

For the inauguration of Barack Obama, she desperately wanted to be among the tens of thousands witnessing the first African American to assume the presidency. Then she thought of how all those people in one spot could make for a juicy target. “I was fine watching it on TV,” she said.

For some, the fear is linked specifically to Sunday, the 10-year mark. Usually, Tricia Siudut, 30, has no problem riding Metro. This Sunday is another story.

“I know we have strong, intelligent people who work hard to make us safe,” she said. “But I’m somewhat afraid to be underground that day.”

The sense that life has changed since the attacks is broad based: More than four in 10 men, women, blacks, whites, immigrants and native-born say the Sept. 11 attacks changed their personal lives in a lasting way. The attacks seem to have had a muted effect only on those 65 and older; almost two-thirds of them report no change in their personal life.

They have lived through war and tumult before. They carry on.

Sherman Cohn, a law professor at Georgetown University, knows exactly where he was when Pearl Harbor was attacked and when President John F. Kennedy was shot. Like after those events, he was affected, and deeply so, by Sept. 11. But he wasn’t about to let it interfere with daily life, and any vigilance he carried around was natural street smarts — not fear of terrorists.

“We all have a little more of a consciousness of the possibility of some incident,” he said. “But those of us [who] have lived in Washington have lived with that forever. When I walk down the street at night, believe me, I watch my back.”

He prayed at New York’s Ground Zero for those who had lost their lives. Sept. 11, like the other major historical events of his lifetime, “had a profound impact on the psyche of each of us,” Cohn said.

“But that was not the question,” he continued. “The question was how did it affect my life. And the answer is, very little.”

How old were you? Multimedia: The Age of 9/11

Special report: Ten years later

Interactive: The Pentagon Memorial

Staff writer Jimm Phillips contributed to this report.