"You don't know what they want to do or how long it will last. If they are going to kill you, release you or sell you to another terrorist group," Angel Sastre said in an interview with online newspaper El Español.
"The simple idea that they could sell me to Daesh terrified me," he added, using an Arabic acronym for the Islamic State group.
Sastre, 35, was kidnapped along with two other Spanish freelance journalists on July 13, 2015 in the northern Syrian city of Aleppo by the Al-Nusra Front, Al-Qaeda's Syrian affiliate.
The three experienced conflict zone reporters were flown to Madrid on Sunday on a Spanish defence ministry jet sent to Turkey to bring them back.
Sastre, 35, said he was allowed to watch the news by his hostage takers after his fourth month in captivity.
"With CNN or the BBC, we learned how the war was going on around us, because Syria was in the headlines almost every day. It was like living inside a bubble inside the conflict," he said.
"I will not return to Syria, at least not for the moment. It is impossible to work there now. Kidnapping is no longer a weapon of war, it is a profitable business," he added.
"You can't trust anyone and anyone may sell you. The translator, the driver, the fruit salesman... it is not safe to work there."
The Spanish government has not disclosed any information about how it won the men's freedom.
The Islamic State group, Al-Nusra's rival, has executed many of its hostages.
In August 2014 it murdered US journalist James Foley, who was taken hostage in northern Syria in 2012.
The following month, the group killed fellow US journalist Steven Sotloff.
In 2015, militants from the group beheaded Japanese war correspondent Kenji Goto.
Media rights group Reporters Without Borders (RSF) in 2015 ranked Syria as one of the most dangerous countries in the world for journalists along with Iraq.
It says 139 journalists died in Syria, where various armed factions have been battling President Bashar al-Assad's regime and each other since 2011.