Sally Lane told jurors her son had initially gone to Jordan and Kuwait for study and tourism.
The mother of a young Muslim convert dubbed Jihadi Jack has told jurors she was horrified when her son called to say: "Mum, I'm in Syria."
Former fundraising officer Sally Lane, 56, and organic tenant farmer John Letts, 58, are on trial accused of sending or trying to send sums totalling £1,723 to their son even though they had every reason to believe he had joined Islamic State.
Jack Letts was 18 when he left home in Oxford and travelled abroad, married the daughter of a high-ranking tribesman in Iraq and moved to Syria, jurors have heard.
His parents allegedly ignored repeated warnings that they faced prosecution if they tried to help their son while he was in IS territory.
Giving evidence at the Old Bailey, Lane told jurors her son had initially gone to Jordan and Kuwait for study and tourism.
She said: "He seemed like he was enjoying himself, relaxing and enjoying the country."
But on 2 September 2014, phone records showed a flurry of calls.
Lane said: "That was the day I found out. Jack phoned me. I was alone in the house. It was just a very quick phone call. He said 'Mum, I'm in Syria'.
"I was horrified. I screamed at him, 'How could you be so stupid? You will get killed. You will get beheaded'."
Afterwards, Lane said she was "off work" and thinking about going to Turkey as other parents had tried to do.
Jack Letts, who is said to suffer from obsessive compulsive disorder, did not phone again until September 24 2014.
Lane said: "That was the first time I heard from Jack after that first phone call on September 2.
"He apologised for not having phoned since that call. He said he had been ill. He had been travelling.
"He did not say exactly where he was. He tried to be reassuring, saying everything is fine. It's a civilian area, it's not a war zone.
"Someone had looked after him when he was ill and not to worry."
Defence lawyer Tim Moloney QC asked: "How did all that contact make you feel?"
Lane replied: "In the first few weeks, we did not know whether he was alive or dead. At least we were reassured he was alive. I had done a lot of reading up on what groups were there."
She told jurors she had been worried that Syria had made her son's "mental illness" worse.
Jurors heard that the defendants' home was first raided by police on March 31 2015.
A month later, Lane attempted to use a £5,000 inheritance from her son's grandfather "as a bribe" to encourage him and his new wife Asmaa to get "somewhere safe".
But on May 21, he posted a photograph of himself in Raqqa, Syria.
Meanwhile, the family continued to have "acrimonious" religious and political debates.
Lane said: "It was a bit different when he is actually in the region rather than in our kitchen."
On July 30, she said she felt "sick" when her son appeared to threaten to behead an old school friend, Linus Doubtfire.
Mr Doubtfire had posted a picture on Facebook as he completed his Commando Artillery Course in the British Army.
Jack Letts commented: "I would love to perform a martyrdom operation in this scene."
His mother told jurors: "I thought it was not him because it was a public post. Jack had told me that other people used his account.
"Around this time also we were receiving false information. I received a message on an account saying he was dead, for instance."
Asked how she felt about the post, Lane said: "Absolutely sick. It was so out of character. He had never said anything violent before. I just thought it didn't sound like him."
Letts and Lane deny three charges of funding terrorism.
The trial continues.
PIC: Counter Terrorism Policing South East/PA Wire