Horrible dream - but of someone else.

This actually happened -

The sister of my (Irish) (artist) friend lived in London for years, and would bike home through a poorer neighborhood where a bikepath had recently been put in by a canal.  The kids would snow snowballs with stones in them at bikers, and one time she was biking and 3 tall older teenagers stood across the path, asked her if she liked to swim, then pushed her and her bike into the canal when she tried to ride past...

She said the canal was only like chest deep, but you never knew what kind of stuff might be in there, the water was so murky.

This was her dream -

For years afterwards, and still occasionally, she dreams she falls into the canal on her bike, and a bike spoke from hidden rubbish in the canal pokes between her ribs deep up into her chest.

She always wakes up immediately, terrified and not sure if it just actually happened to her.