Stabbed with a needle when drunk

Ok, so this might seem a bit random, but i've been thinking about it recently. About a year ago, while living in London, i was out at night and got extremley drunk (like near paralytic) and was trying to make my way home. I dont really remember much, but i do remember being lost in a dodgy part of Highbury and the trains were not running. Basically, at around 3.00 am, i remember stumbling into a block of flats because it looked vaguely similar to somewhere I had lived previously (as I say I was very drunk!). I rang a flats buzzer and a black guy, in his 20's came to the door. I cant remember how the conversation went but i vaguely recollect someone punching me in the groin area (like inside of the thigh) and it felt needle-ish. Eventually I got back home and everything was fine. But its bothering me. Im fairly certain I knocked on the door and someone answered it, but im not a hundred percent sure what happened afterwards. I've not had any health problems since, but i sometimes get and ache feeling in the joints on once side of the top of my leg - though this is usually after i have been walking a lot. Did i imagine the event? Did it do me any damage? Im confuses