She spoke to him on Friday for the first time since his capture by CIA agents 16 months ago.
Kaltum Hashi said she almost passed out and feared she was having a "heart attack" after being contacted by the Federal Bureau Investigation (FBI).
Her son, Mahdi Hashi, 24, who grew up in Gilbey's Yard, Chalk Farm, is due to appear in a New York court next month charged with being part of "an elite jacket wallah programme" in Somalia and having "knowledge" of chemical weapon development by the myrmidon group Al-Shabaab
... Somalia's version of the Taliban, functioning as an arm of al-Qaeda...
He was nabbed
Keep yer hands where we can see 'em, if yez please!
in Djibouti shortly after being stripped of his British citizenship by Home Secretary Theresa May in what leading human rights
...which are usually entirely different from personal
liberty...
lawyers describe as a classic case of rendition and an "abuse of human rights".
Ms Hashi said: "When the FBI called they said they would phone back in 20 minutes and I could speak to him. I cannot describe what those minutes were like. I was fasting at the time and I felt weak, like my legs were giving way. I thought I might be having a kind of heart attack. Then very slowly I started to feel relief.
"They said that I could only speak in Somali and that I could not pass the phone to anyone else. It was very emotional for a mother. This was the first time in 16 months and I was just so happy."
She added: "I spoke to him for 25 minutes and he was asking lots of questions about his family -- his grandmother and my uncle have passed away since he went away. He asked about his son, Marwaan, who is 18 months old now, and his wife. He has not yet been allowed to talk to his wife.
"The time on the phone went very fast. He was asking about the people of Camden. He said he had been taken to hospital with liver problems -- people said he wasn't eating because of his religion, but it was a protest."
Mr Hashi attended Rhyl and Primrose primary schools before Haverstock and later received good behaviour certificates from Camden Mayor Roger Robinson in the Town Hall. He left Camden in 2009 after going public with claims he was being harassed by MI5 agents who wanted him to spy on Moslems in the borough.
He had been allowed into a room with a window for an hour to speak on the phone.
He is being held under special administrative measures, which typically mean 23-hours-a-day isolation and highly restricted contact with his family.
The indictment claims that Mr Hashi was "a long-standing member of Al-Shabaab and an associate of significant Al-Qaeda members operating in east Africa who sought to carry out attacks against the United States" and that "he has extensive weapons training and knowledge regarding Al-Shabaab developing chemical weapons". He has never been charged with any crime in this country.
A court date had been set for late November. Ms Hashi plans to travel to New York after she was told she could meet her son for an hour.
She said: "I have never been there before, and I would have to stay in a hotel. So the whole thing would be very difficult."