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A mother woke up in the night to find her 14-year-old son raping her, a court heard.
Initially she thought it was a dream, but after realising the "enormity of the situation" she began screaming.
Her teenage son, who is on medication for ADHD, had been having behavioural problems in recent weeks, Preston Crown Court was told.
For some years he had been in the habit of climbing into bed with his mother, but the boy - from Blackpool and now aged 15 - denied a charge of rape.
Francis McEntee, prosecuting, told the court: "The allegation in this case is that the defendant raped his mother while she was asleep. The factual basis of this case is that he was in his mother's bed.
"The issue is not any assertion of consent, or belief of consent. It is the prosecution's assertion there was penetration and the defendant's denial of that allegation".
The prosecution said the woman had been asleep before waking and realising the "enormity of the situation, that her son was in the process of having sex with her".
Mr McEntee added: "The defendant's account is that his bed was uncomfortable, there was damage to the bottom sheet, so he had gone in and lain in bed with his mother."
He told the jury: "You will hear his acknowledgement that his mother was naked, bar the brief underwear and you will hear his admission that she lay on her side and he was lying with his arm around her.
"The prosecution would invite you to say he was hoping to seek to try and provide an innocent explanation for his presence in the bed. Whether driven by drink or some other issue, perhaps because he had had drink, he climbed into bed with his mother".
In her video police interview played in court, the woman described herself as "trembling from the inside".
The youngster, who cannot be identified, chose to leave the courtroom while the interview was played. Judge Pamela Badley told the jury he had not wanted to be present at that stage and she had given him permission not to be there.
Speaking of what happened, the woman told police: "I just know when I opened my eyes he was there. I don't even know what I said. He scuttled out of the room and didn't say anything.
"I just sat there holding my covers, screaming and thinking 'what the hell's just gone on?'
"All sorts was going through my head. Is he just sleepwalking?
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"Does he know what he is doing? Is he aware? Now I am actually thinking what state is he in? Does he know what he has done?"
The middle-aged woman went on to tell police that her son had had issues for a long time and the last 18 months had been an "absolute nightmare" that had been getting worse.
She also said in her interview: "He's really aggressive towards me, throws things and hits me with things like slippers and cushions. Only two days ago I got cut. This is me trying out ground him and instil some punishment for the way he has been."
At the end of the interview, she added: "I am concerned for my son, more concerned about what would happen to him."
The trial continues.