From
Arthur C. Clarke's
The Deep Range.
The Deep Range is about, among other things, farming the sea. One of the methods of sea farming used is the farming of whales for food, in a process similar to cattle farming. This process requires the presence of "sea cowboys" (whaleboys?) to herd and protect the whales.
The whaleboys spend a lot of time with the whales in tiny submarines (40 feet is the given length). As you might expect, this leads to a feeling of oneness with the whales. Some of the more experienced whaleboys (whalemen?) become so attached to the whale herds that they only feel happy when with them. This is know as being "whale happy". In extreme cases, whale happy people will only feel comfortable if they rise to the surface when the whales do so to breathe, and dive when the whales do. Whether any whalemen have disappeared into the ocean night with the whale herds, never to be seen again, is undocumented.