How does James Herriot use imagery in The Lord God Made Them All?

Imagery:

"It is interesting to note that the only time I felt strange was when I struggled up to the deck for some fresh air and stood for some time looking out on the crazily swinging sea. After a while, as I hung onto the rail, I began to experience a sort of dizziness. It was a visual thing, brought on somehow by watching the constant lifting and falling of the world about me, but it wasn't pleasant and I went back to my cabin."