07/04/2014 07:19 BST | Updated 07/04/2014 16:59 BST

Oscar Pistorius Weeps And Cries 'God Help Me' As He Takes The Stand, Apologising For Reeva Steenkamp's Killing

Oscar Pistorius has told his murder trial in South Africa that there is not a day when he does not think of his girlfriend Reeva Steenkamp and her family, saying he wakes up terrified every night.

As he took the stand his first day on the stand at his trial for Steenkamp's murder, Pistorius whispered, his voice trembling and tears streaming down his face, "God help me".

"I would like to take this opportunity to apologise to Mr and Mrs Steenkamp, to her friends and families," he said, pausing often to catch his breath.

Oscar Pistorius in court for the first day of the defence

Looking over at the Steenkamp family, Pistorius said: "There has not been a moment since this tragedy that I don't think about her family. I wake every morning and you are the first people I think about and you're the first people I pray for. I can't imagine the pain and sorrow and emptiness I have caused you."

Pistorius denies killing his girlfriend deliberately on Valentine's Day 2013, saying he thought she was an intruder when he shot her through the bathroom door.

"I was trying to protect Reeva", he said. "I can promise when she went to bed that night she felt love."

South Africa has no trial by jury, and Judge Thokozile Masipa will decide whether Pistorius is guilty or not guilty of murder. The trial is resuming after 10 days recess, because of a court official's illness.

Asked whether he had trouble sleeping, and whether he took medication, Pistorius said he had been on anti-depressants for 14 months. "I am scared to sleep. I have terrible nightmares," he said.

"I always lie awake in a complete state of terror, I would rather not fall asleep than wake in terror. I wake up with the smell, the smell of blood.

"In March and April I lost a lot of weight, I sought medical advice for sleep deprivation."

He described how he climbed into a cupboard one night in a panic attack, and had to call his sister to come and look after him. "I never want to handle a firearm again," he said.

The Paralympic athlete was first asked to describe his childhood and the difficulties he encountered when his legs were amputated because of a missing fibula in both legs, and the amputation of his legs below the knee when he was 11 months old.

Pistorius said he did not feel vulnerable with his legs on, but on his stumps he felt he had "difficulty with balance and limited mobility".

Sport was his family's way of making him feel like a normal child, and he was encouraged to "stand up for himself," he told the court.

As a child, Pistorius said his mother became very frightened of intruders when his father was away. She kept a firearm in a cushioned bag under her pillow, Pistorius said, and because they didn't live in the "best of suburbs" in Johannesburg, they had a number of intruders enter the house.

Asked to describe the death of his mother, Pistorius called her "a very important person to my brother, sister and I."

"My parents got divorced when I was quite young, and my father's family kept in close contact, she had a loving relationship with all of them," Pistorius said.

"Everything I learnt in life, I learnt from her. It was very unexpected when she passed away. I had just started boarding school, she had just got remarried.

"My brother and I didn't know she was sick. By the time we were informed she was already in a coma. Then later, we got a call at school telling us to come to Johannesburg and we were there for about 10 minutes before she passed."

He talked the court through developing his sporting career, first in rugby then in athletics, and mentioned his frustration at not being able to run able-bodied races in 2008 at the Beijing Olympics, called it a "big disappointment for me" after he failed to qualify by half a second. He qualified for the London 2012 Olmypics, and represented South Africa, he said.

'I have a lot of problem with skin irritation inside my prosthetic legs," he said when asked about his injuries, saying the skin inside the prothesis often repeatedly fell off.

He said that he took the prosthetics off at night to "let the stumps breathe" and said he found that hard while travelling. He got infections and blood clots, he said.

"I don't have balance on my stumps, I can't stand still on my stumps," he said. "They are by the bed, and I put them on when I wake up. I might not put them on in the night when I want to stretch, or if I wanted to fetch something quickly but not often.

"I have to stand holding on to something or move constantly," he said, when asked if he could balance on his legs. "My dog could knock me over".

Pistorous went on to describe a serious boat accident, when he was hit in the face with a propeller in 2009. "I was pretty much drowning on the blood from my head injury," he said of the accident which left him in an induced coma, and led to him having more than 170 stitches.

"It was a massive impact on me. I was fearful, withdrawn. I nearly lost my life," he said, adding that it led him to become more vigilant about personal safety.

"I wouldn't leave my prosthetics lying around, I keep them close to me all the time, close to my bed," he said, adding that he stores them one on top of the other. He called the legs an "extension of myself" and said he would not want to be seen without them.

After an hour with Pistorius on the stand, the judge called a break for lunch. The trial continues.