Hip Priest
Veteran
Sounds to me like over training - doing too much too soon.It is the inability to recover from the cycling rather than the cycling itself I am guessing.
It is important that he replenishes his glycogen store within two hours of completing his ride. As you are on holiday and maybe camping (I don't know) get some of that Ambrosia rice in a tin and get him to eat one of those straight from the tin. If you have access to a kitchen you can get some quality carbs down him - not sugar - complex carbohydrates.
No disrespect to the OP's hubby, but he's doing 11 mile rides. He isn't overtraining.