Immediately a nightmare scenario rolled across my brain in which my possessions spent their day trundling around Network SouthEast while I tried frantically to trace them.
I sprinted back across the concourse and panted "Train that just came in - left my bag," at the guard on the gate, who let me through.
Against all odds I remembered which platform I'd arrived at and stepped on board the right carriage, snatching up my bag to the enormous amusement of a cleaner who was emptying the bins.
When I exited, the guard told me to be more careful next time as I could have caused an evacuation. I apologised profusely. He said: "All right, babe. All is forgiven!"
Serves me right for putting my luggage in the luggage rack. Next time I'll take up a whole seat with it like every other bugger.