yes this kind of thing does happen (example around here on the college campus there is a problem with frat parties and the use of rohypnol and other drugs being slipped into drinks so that the perp can follow their victims home wait until they are passed out then enter and have their way)

but this kind of thing leaves a trail which is why victims get a very special exam in the ER. not all evidence washes away. theres internal bruising, tearing, and other internal physical evidence, plus there is also external physical evidence that says whether a person has had sex and whether it was consensual or not.

even people who have been drugged know whether they have been abused in their sleep or not. you would have known whether you were abused in your sleep three years ago.

one way you can verify for yourself is contact your treatment providers they can look back on their records and see whether you had any of the physical and mental evidence that this kind of thing leaves behind and whether you were seen in the ER or other mental health treatment providers for things that come as a result of this.

you can also contact your therapist or other mental health treatment provider who can look back on your files to see what you told them from back then, there will be documentation of something like you waking up feeling something had happened and what evidence you shared with treatment providers.