By any measure, Dr. Osman al-Haj Osman has been a success among the tens of thousands of Syrians who have streamed into Europe. He received asylum in Germany. He's taking lessons in the language, is getting help from the state in finding a job and was able to bring wife and kids to join him.

But the 33-year-old surgeon is haunted by doubt over whether he made the right decision for his family in immigrating to such a different world. He's also burdened by memories of his country's civil war and the way in which his two young sons were branded by its horrors before they fled his home city of Aleppo in northern Syria more than a year ago.

"Everything around me, I feel, is temporary. Until now, I find it really hard to write my home address as anywhere other than Aleppo," he said on a rainy afternoon in September in Saarlouis.

In 2012, Osman was the senior doctor at a front-line hospital in a rebel-held district of Aleppo under siege by Syrian government forces. Round the clock, casualties flowed into the Dar al-Shifaa hospital, civilians and rebels, wounded or dying in the intense urban warfare and heavy bombardment by Syrian forces.

Looking constantly exhausted, Osman hardly ever took off his often blood-stained, green surgery scrubs as he and the overwhelmed staff tried to deal with the wounded. "I have to make a choice between a child with a 10 percent chance of survival and one with a 25 percent chance," he told the AP at the time. When a wounded rebel died, often his comrades would burst into rage at the staff, convinced more could have been done.

Osman's wife and two young sons were living in the hospital with him. His older boy, Omar, who was 4 at the time, would walk among the maimed or dying, passing the pools of blood on the floor and the occasional severed limb. He would play in the hospital hallways or make joke announcements on the hospital PA system.

Now looking back, Osman said he regrets bringing his family into the hospital. He'd wanted his wife and children near him, but he said he hadn't realized until it was too late the trauma he had inflicted on his children. The boys now draw pictures of tanks, warplanes, wounded people and wrecked houses.

Omar still has nightmares. Osman recalled running errands in the streets of Aleppo with the boy, who, whenever a plane passed overhead, would ask his father if it was about to bomb them.

Osman recalled another question Omar asked him once. "Papa, who created the world? The person who created it, can't he see what's happening to it?"

Dar al-Shifaa closed in November 2012 after a government airstrike hit a neighboring building, heavily damaging the hospital and killing four inside. Osman eventually worked at a clinic with Doctors Without Borders, known by its French acronym MSF, trying to lay low as Islamic militants gained increasing power in the rebel-held districts of the city.

In August 2013, the militants arrested him, and he was questioned by an Egyptian militant who told him that MSF was headed by a "kafir," an infidel. Later in detention, he heard the Egyptian talking to other militants, telling them they would eventually have to kill him — but not now, they had other priorities. So they let him go. He left MSF three months later.

Finally in early 2014, he fled with his family to Turkey. After months of looking for work, he decided to head for Europe.

His wife had resisted the idea of coming to Germany. Still, she and their kids — Omar, now 7 years old, and Rushd, 5 — arrived in Turkey on Tuesday.

He shares her doubts about life in a different culture.

"Many young Syrians abandon their identity soon after they arrive here," he said, speaking as he was reunited with Mohammed al-Haj, a 26-year-old Syrian who had volunteered in the same Aleppo hospital. Al-Haj had just arrived after a 14-day journey from Turkey across Greece and the Balkans, sneaking across borders.

Now living in the state of Saarland, Osman has applied to two hospitals for jobs. He takes German lessons in the town of Saarlouis, not far from the town he lives in. With asylum, he gets a stipend of around 1,000 Euros ($1,100) a month.

"The situation in Germany is now good for Syrians," he said. "But there are no guarantees it will continue to be the same. What if a terror attack happens and is blamed on Muslims? I must have a Plan B."

Osman believes the danger of Islamic terror on German soil doesn't necessarily stem from the possibility militants have slipped in with the refugees streaming into Europe. He said militant ideas are already here in Germany.

He recounted an incident in the nearby town of Merzig in July when a Syrian man harshly berated a 12-year-old Syrian boy for wearing shorts in the mosque, accusing him of disrespecting the place, leading to a fight with others trying to calm the man down.

Regardless of what may happen, Osman is filled with gratitude for Germany.

"I have a debt to repay to Germany, the country that helped me when no one else did," he said. The stipend, he said, he'll pay back quickly through income tax once he starts working. "But I can never repay the moral debt I owe to Germany."