Oscar Pistorius took the witness stand yesterday in his murder trial and stifled sobs as he apologised to the family of the girlfriend he shot dead.
He described himself as traumatised and said he was now on antidepressant medication.
He also said he sometimes awakes from nightmares to the "smell of blood".
Watch: Distraught Pistorius apologises from the witness stand
The South African Paralympic track star apologised to the mother of model Reeva Steenkamp, saying he had fired four times through a toilet door at his luxury Pretoria home in the belief he was defending her from an intruder.
"There hasn't been a moment since this tragedy happened that I haven't thought about your family," he said as Steenkamp's mother, June, looked straight at him in the courtroom.
"I can promise that when she went to bed that night she felt loved," Pistorius said, after asking for permission to make the apology at the start of his testimony.
"I'm scared to sleep. I have terrible nightmares about things that happened that night," he added. "I can smell blood. I wake up to being terrified."
His voice quavered so much and was so low at the start of his testimony that Judge Thokozile Masipa asked him to speak up.
He recounted one occasion when he woke up so scared in the middle of the night that he crawled into a cupboard before calling his sister.
"I wake up in a complete state of terror to the point that I would rather not sleep," he said. He added that his faith had helped to pull him through.
Earlier, during graphic forensic testimony from a defence pathologist, Pistorius retched into a bucket in the dock.
The distraught, bespectacled figure was in stark contrast to the gun-obsessed, fast-living hothead that prosecutors described in the first 16 days of the trial.
Pistorius' testimony also addressed previous instances of crime that affected the runner and how he felt vulnerable because of them, an attempt to explain his claim that he reacted to what he thought was a dangerous intruder in his bathroom by shooting his 9mm pistol.
He described how his family had "security concerns" when he was young and his mother slept with a gun under her pillow.
Pistorius said his family had been targeted by criminals over the years, citing incidents of house break-ins and carjackings, and said he had sometimes been followed by unidentified people while driving home.
The judge granted an adjournment because she said Pistorius looked "exhausted".
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