On his return to Syria in 2009 however, despite his age and his position as an assistant professor at Aleppo University, in the north, he could not escape the obligatory period of military service.
After six months of training -- "extremely hard", he said -- he was assigned to the army's Third Reserve Infantry Brigade, based in Damascus and under the orders of the presidential office.
Its main mission, he said, was to protect the capital.
"It was nothing but bullying and ill treatment," he said.
"We lived in appalling conditions, with disgusting food, non-existent medical care," said Hassan.
"The senior officers were without pity. It was crazy..."
It was a far cry from what he recalled as his halcyon days in France, studying for his doctorate on 20th-century French poetry.
"The barracks was a prison," he said. They were forbidden to use water-heaters or coffee machines in their rooms. They were not even allowed to read.
"All the same, I read under the covers," he said: a few novels and the war memoirs of French WWII hero, later president, General Charles de Gaulle.
The uprising against Assad's rule began in mid-March, 2011 and the brutal army crackdown quickly followed.
By mid-2011 Hassan had decided to desert the first chance he got -- even though he knew he would be executed if caught.
But finding an opportunity was not easy. It was impossible to even get clearance to leave the barracks, which were in a suburb of the capital.
Nor did it help that he was not well thought of by his senior officers, he said: they disdained his foreign education and his health problems.
And to make matters worse, his passport was confiscated in the summer of 2012.
Then, on July 8, he was assigned to accompany his colonel into Damascus.
That same day, he made up a story to get away and headed straight for the bus station, meeting up with two fellow officers who had also decided to escape.
From Damascus, they travelled northeast to Al Thawrah, where Hassan came from -- and where he was counting on contacts from the rebellion to help escape to Turkey, further north.
He carried only his officers' papers and his little brother's identity card: and with no papers setting out orders from his superiors, he had to avoid military checkpoints.
It took two days to make it to Turkey he said -- and it was touch and go all the way, dodging check points on the road and several times having to flee pro-Assad forces.
Once he reached the border village of Atme, he was approached about joining the rebel forces, as an officer. "Out of the question," he said.
He made it over the border and now stays at an appartment in the Turkish border city of Reyhanli, where some of the tens of thousands of Syrian refugees who have fled to Turkey have gathered.
He and his two companions -- one an artillery office who like him is a literature graduate, the other a military doctor -- help treat the wounded, who are crammed into a non-descript building not far from the city centre.
"We help each other out," he said, describing the collective life that has developed there.
But while he is considered a guest of Turkey -- a harsh critic of Assad's crackdown -- he has no real legal status.
His ordeal has only made his health problems worse, but without his passport Hassan can travel no further.
He still dreams however of one day being able to return to France and get treatment.
He would like to be able to breathe, "the air of freedom" once more, he said.