Did I consent

So I’ve had a relationship with a guy whilst being at uni, whom uses drugs frequently. He turned up to my flat once with a knife and overdosed on Valium. Anyway one night I took Xanax (it was my first time taking the drug), and he didn’t have one with me but claimed he’d already taken one earlier. Anyway I can remember him pinning me on the bed and slapping me on the bum (until I had bruises), I remember asking him to stop but he carried on - at that point I think the Xanax kicked in and I think we had sex as I can briefly remember bits but I do not by any means remember giving consent. I’ve asked him about it, and he changed the subject I was just wondering what that situation should be considered as?

So I’ve had a relationship with a guy whilst being at uni, whom uses drugs frequently. He turned up to my flat once with a knife and overdosed on Valium. Anyway one night I took Xanax (it was my first time taking the drug), and he didn’t have one with me but claimed he’d already taken one earlier. Anyway I can remember him pinning me on the bed and slapping me on the bum (until I had bruises), I remember asking him to stop but he carried on - at that point I think the Xanax kicked in and I think we had sex as I can briefly remember bits but I do not by any means remember giving consent. I’ve asked him about it, and he changed the subject I was just wondering what that situation should be considered as?

In your post I'm boldening all the stuff that's obviously rape/sketchy AF. ^

http://hr.qmul.ac.uk/media/hr/docs/equalcommittee/reports/Consenting-To-Sex-A4.pdf
Pg 3: Can someone agree to have sex if they’re drunk or have taken drugs?

TLDR: If you're of relatively stable mind and can make free choice and at that moment you say yes then you can consent. Obviously you were not and so it was rape - "at which point the "xanax" kicked in and I can't remember it"

Also, you "asked him to stop" he didn't. Hence rape. That's quite obvious and clear cut.

Also, with the giving you a xan. He didn't take one with you because he "took one earlier"? How do you even know that was a Xan and not a date rape drug? The fact it could be a rape drug is further shown by him not taking one with you..
Call the police on this guy and cut all contact with him, he doesn't sound like anyone who's even slightly pleasant to be around. I want to fully hammer in the fact that this entire story was obvious rape, doesn't matter if he was mentally impaired at the time himself, tell the police. The fact you're asking online when it's this obvious shows that you're probably in denial about being raped. You did not consent. You were raped. End of story.