It is impossible to imagine. Falling back towards the coast along roads clogged with military traffic and refugees; under heavy air attack and outnumbered by an enemy close behind. Once on the beaches a wait for, possibly, several days to be evacuated. Still under frequent air attack and, in the later stages, subject to artillery fire.
Once aboard a ship you were still not safe. The Stukas kept coming and many ships were sunk. If you were lucky another ship would pause to pick you up.
A short dramatised video, complied from the memories of a number of men who were there, has been added to our Dunkirk history page courtesy of the producers. It's not directly related to Medway Queen but take a look and if that gets you thinking it's not too late to get a copy of our own "Memories of Dunkirk" book in time for Christmas.