Oscar Pistorius began testifying in his murder trial on Monday, apologizing to the family of Reeva Steenkamp, the girlfriend he killed last year.
Pistorius said he is on anti-depressant medicine and had sometimes woken up in terror because of the trauma of the shooting.
"There hasn't been a moment since this tragedy happened that I haven't thought about your family," the double-amputee runner said when he took the stand. "I wake up every morning and you're the first people I think of, the first people I pray for."
Pistorius, who has said he shot girlfriend Reeva Steenkamp by accident after mistaking her for an intruder, also said: "I was simply trying to protect Reeva."
He said Steenkamp, a 29-year-old model, felt loved when she went to bed on the night he killed her. Prosecutors alleged he killed her in the early hours of Feb. 14, 2013 and have sought to paint him as a hothead with an inflated sense of entitlement and a love of firearms.
Pistorius said he "had tried to put my words on paper many times" and said he had been on medication since shortly after the killing and has difficulty sleeping. He described one episode in which he woke up in a panic.
"I climbed into a cupboard and I phoned my sister to come and sit by me, which she did for a while," he said.
"I'm just in a complete state of terror," he said. "I fall asleep and wake up like that."
Pistorius has been charged with premeditated murder. He faces 25 years to life in prison if convicted of that charge.