Nope. The shock is a medical possibility if you accidentally fall in Arctic water or something like that, but it’s not something that will come up in a swimming pool scenario unless you’re doing one of those influencer ice baths or something of the sort.

It’s mainly caused by extreme sudden temperature change, not much to do with the stomach.

Funnily enough, even medical pages in Spain will talk at length about the medical phenomenon without mentioning that little detail.