"He went back to prison after the questioning but he continued to feel ill and he was taken to the prison hospital in the afternoon," said one of the sources on Tuesday, who asked not to be named.
Nur, a parliamentarian and leader of the opposition Ghad (Tomorrow) Party, has been detained since January on allegations of forging documents to officially register the party. He denies the charges.
Interior Ministry officials said Nur's life was not in danger and his condition was linked to his diabetes, for which he was receiving medication.
Nur's wife, Gamila Ismail, told Reuters Nur had fallen ill during questioning at a State Security Prosecution office in the early hours of Tuesday.
"He was sweating, vomiting and holding his left arm"
"He was sweating, vomiting and holding his left arm," Ismail said, adding that Nur has a history of diabetes and heart problems.
She said Nur began feeling pain at 1.00 am and his personal doctor advised he be taken to a nearby hospital.
Ismail said officials made no decision until three hours later, when they decided Nur could go to the prison hospital. But initially he declined to go, she added.
The government says Nur's detention is a criminal matter relating to forged documents. Nur's supporters say the charges are fabricated for political reasons.
The United States has expressed "very strong concerns" about Nur's detention but Egyptian officials have said foreign intervention in internal affairs is unacceptable.