Saber Lahmar explained that he was deprived of sleeping and food and there was constant noise from a motor outside his door.
“You couldn't walk, move, talk -- it was forbidden,” said the 42-year-old Algerian, who successfully appealed for freedom in a civilian court in Washington in 2008.
The court found no evidence of Lahmar's alleged crimes or that he was a threat to the United States.
Lahmar, who arrived in the prison in January 2002, also said that he was subjected to electric shocks and there were drugs in his food, which stopped him sleeping.
He noted that he was subjected to constant glare of florescent light in a metallic cell measuring two meters by 1.5 meters (six feet by 4.5), with freezing, constant air-conditioning.
"For a year and a half I didn't see the sun," he said, adding that he was made to sit on a stool for 18 hours at a time during interrogations.
After the September 11, 2001 attacks, hundreds of people were sent into the black hole of the military prison at the US naval base in Guantanamo Bay, Cuba.
There are still 171 men in the prison despite vows by US President Barack Obama to close the notorious prison.