This will be outing so I'd better name change soon! But I experienced a time slip in London about 15 years ago.
I was sent on an errand to another office so left work on a bright clear day. I worked in the Cheapside area of the city - where a Christmas Carol was set. I walked up Cheapside/ Poultry in the direction of Bank of England. To my left was a street that was either Old Jewry or the street adjacent to it. So I take a short cut up that street. Nice day, escaped from the office, stills fairly new to London and loved it - all was good. Walked up the street, all fairly bland offices, modern and tall. I was the only person on the street. Suddenly out of nowhere I felt the most indescribable terror come out of nowhere - I almost expected to hear someone shout 'run'' It felt like something or someone was coming for me. I glanced at the offices but suddenly they were different - they were lower than ground level so that the pavement bisected the windows, and the buildings were now old - they looked like old fashioned sweet shows with those windows with the small square panes and occasional round bit jutting out. All around me I could hear noise - hustle and bustle, hooves on cobbles, barrels rolling, voices talking and shouting out to each other. The sky was dark and the air thick with a brownish mist (smog?) My head was hurting and I just lost it and ran towards the end of the street like my life depended on it.
And then everything was normal. Sky was normal and blue and clear, buildings were as they should be, no noise out of the ordinary. My headache went instantly, my feeling of terror went instantly - I felt completely ok. Freaked out by what just happened but completely my normal self.
The funniest thing was there was a chap smoking across from me and as I stood there baffled he jumped a mile and said 'where the hell did you come from?!' When I told him he said he'd literally just walked out of there and there had been no one there - so now as well as my own time slip I wonder if I feature in some bloke's story about the girl who appeared out of thin air!