@Claire that sounds terrible. I hope you're ok!
In February I had my chain get stuck somewhere in the drivetrain which locked the pedals and wheels and threw me off the bike (I was clipped in) as I went round the roundabout at the bottom of Broughton Street.
I rolled down the hill to EBC and they rejoined the chain with a power-link thing and got on my way to work (very late!).
Two weeks ago the chain snapped again as I moved off from the lights on North Bridge / Princes Street. I stopped outside the St James' centre and tried to rejoin the chain using a chain tool, only to find part of it was missing!
I rolled/walked to EBC and got a new chain put on.
The next day I got a puncture from a teeny tiny piece of glass that had got through the tyre.
So over the last week I have replaced the chain, cassette, both tyres (for Conti gatorskins), all brake shoes & pads, brake & gear cables, and grip tape.
It's nice to have done all the work myself, and it feels like a new bike!