I guess I disagree with Mark when he says an initial fear is of dropping the
seat. At first I was far too concerned with staying alive to be worried
about the seat.

Much more sensible to be worried about your foot slipping off the pedal and
getting caught in the spokes (happened to me - that’s why I started wearing
shoes :-)). Not to mention cracking your head open or smashing an elbow as you
fall backwards, or falling off as you cycle on the side of the road as the cars
go rushing by…