A teenager has been found not guilty of raping his mother as she slept after she told a jury she had dreamed the attack.The boy, who cannot be named, was 14 when his mother woke up and accused him of trying to rape her.

Despite calling the police to report the alleged incident, when the case reached trial this week the mother claimed she was “99.9% sure” she had dreamed it after a night out drinking.

She blamed the episode on her mental health problems and the stress of trying and failing to get help for her “difficult” son, who has Asperger syndrome and attention deficit hyperactivity disorder (ADHD).

Her son always denied the charge, saying he had got into bed with her as his own was uncomfortable.

She told police: “I just know when I opened my eyes he was there. I don’t even know what I said.”

Yet more than a year later, when called to give evidence as the prosecution’s only live witness, the woman said she did not want the case to proceed.

Under oath, she said when she called 999 she was “a woman on the edge”. She insisted her son had not raped her. “I just think I was having a dream and [the boy] has cuddled into me,” she said.

“I’m 99.9% sure that it was a dream,” she said later, comparing it to an earlier “sexualised dream” she had about a neighbour in 2005 which was so vivid “I couldn’t look him in the face for weeks”. The neighbour was not in her bed at the time. “Normally, I wouldn’t look at him twice,” she told the court.

The boy, now 15, did not give evidence during the two-day trial at Preston crown court.

But in an interview with the police after his arrest on 23 February last year, he said he often got into bed with his mum. “I’ve always been a baby like that,” he told detectives.

He said he climbed into bed with her after hearing her return home drunk from a night out with friends. He claimed to have got under the covers, put the TV on and dozed off with his arm around her when she suddenly shouted: “What the fuck do you think you’re doing?”

In a police interview played to the jury on Wednesday, recorded the day after the alleged rape, the mother said: “I woke up and found my 14-year-old son on top of me.”

The court heard she had a history of mental illness and suffered a bout of psychosis aged 16 or 17.

Under cross-examination on Wednesday she said she felt she had been suffering “some sort of breakdown” at the time of the alleged rape. “I had had a horrible 18 months. I had been trying to access help for my son,” she told the jury.

She said six to eight weeks after making the rape complaint she had tried to withdraw it but no one listened. On giving evidence in court she said: “I just feel I’m not being listened to. I feel like I’m being railroaded.”

Francis McEntee, prosecuting, suggested she was lying to protect her son from going to prison. The mother responded angrily: “I’m telling the truth, the whole truth and nothing but the truth. This didn’t happen and my son has been failed by this system that’s quite clearly fractured.”

Her son was discharged after the not guilty verdict was returned.

Afterwards, a CPS spokesperson said: “A charging decision was made in this case after consideration of all the evidence, which we considered to be sufficient for a realistic prospect of conviction. This was an allegation of a very serious offence and it was important that the jury heard all the evidence and was able to make a decision in this case. We respect the jury’s decision.”