The then-21-year-old woman stayed at a friend's house in Hamilton following a birthday celebration.

She woke to find a man she knew naked in her bed and touching her underneath her clothes.

The impact of the crime on the victim was heard in Warrnambool County Court on Monday where the 23-year-old male offender pleaded guilty to sexual assault.

In her victim impact statement, the woman said she now suffered frequent panic attacks, which at times left her housebound.

She said during the attacks she was hyper-aware, self-loathing and scared of crowds, especially if there were men.

"I get extremely frustrated and angry at myself because I can't do things I want to," she wrote.

"I want to be this strong independent woman but in these moments, I couldn't be further from that version of myself and that's heart-breaking for me."

The victim-survivor said she felt like a "shell of my real self" and rarely travelled back to her home town, causing childhood friendships to strain.

She said at times she felt the only way to be sure she would never be sexually assaulted again was to take her own life.

"I didn't feel this scared to exist before this assault," she said.

A prosecutor told the court the offender and victim were known to each other and she had allowed him to sleep in the same bed as her after reiterating a "no touching" rule.

Despite her requests, he said the offender had taken advantage of a vulnerable, young woman.

A lawyer for the offender urged the court to consider a non-custodial sentence, saying the sexual assault was "very out of character" and his client had good prospects of rehabilitation.

Judge Gregory Lyon ordered the man be assessed for a community correction order, proposing a lengthy number of hours of unpaid community work and a men's change program.

"Time and time again in this court I find young men like you sitting before me and the problem I find is a fundamental lack of understanding of the need to respect fellow human beings and particularly women," he said.

"You've heard the effect of your offending on (the victim). There'll be a day when you'll be free of this and I don't know if I can say the same about her.

"You did that to her. You and thousands of men across this state and country and across this world just keep imposing your will on women and you know what, it has got to stop."

The man will be sentenced on Wednesday.

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