Sounds like there was more going on than just hypothermia. You may have come down with a flu or some other disease. I've sen it quite a few times and been through it myself once or twice. I'm feeling strong and them ...whammo ... it is like someone pulled the plug. Fortunately it never happened in the backwoods.

I once had a friend suffer such an onset during a trip. His was pretty clearly the flu that was going around. About sunset he lost power. He couldn't eat, had chills, a high fever, and generalized weakness. He could barely stand. Fortunately we were close enough in that it wasn't a big thing to get him to a road and get us picked up. This was before cell phones so I hiked out the few miles to call a friend.

Doctors said that physical exertion, heat of the day, and possible borderline dehydration made it worse. As it was he was good to go after a few days sleeping in and mothering by his girlfriend.

I'm no doctor, and I'm not going to second guess your judgment. Sounds like there was more than just hypothermia. Uncontrollable shivering is common but serious cramping seems out of place.

I suspect that you exerted yourself far more than you thought. That you were close to exhaustion but perhaps fooled by cooled temperatures, sunshine, into thinking you were less tired than you really were. I've seen this during early season trips when people mistake the signs of exhaustion for 'being a little rusty'. If you fell in while near exhaustion the effect could be profound. In effect all systems would be demanding energy you don't have. Throw in a little dehydration and not eating enough and you are looking at the mother of all Bonks.

It also should be noted that this is the beginning of the cold and flu season. Add a virus to the above and it gets bad, Very bad. What happens if you hadn't got out of the water? Body recovery is a bummer for everyone involved.

Calling for help is okay. Doing it before you are absolutely sure it is clearly a life and death situation is okay. That is why those guys are there. Why they make the big money and get to play with the shiny toys. You had good reason to think it was potentially life threatening and acted accordingly.

Rule Number One: Don't let what anyone else might think keep you from doing what you have to do. You have to make your own call. Embarrassment and shame pass. Death and serious disability ... not so much.

From your previous posts you seem to have your duckies in a row. It isn't like you stubbed your toe and had the National Guard fly to Timbuktu to give you a taxi ride out for convenience sake.

And yes, the Coast Guard seems to have only two settings, all out and off. They seem to figure that it is better to go big and back off if reasonable than go small and find out they don't have enough resources. I bet you most of the crews were sitting around bored. A bit of pre-season warm up probably did them some good.

Glad it worked out.