I’m sorry but this thread is full of bad advice, it is only right that you should be informed of that. If you choose to take said bad advice, that’s your call, but do it for the right reasons - not because you don’t like my attitude.
The notion that a 100km ride could cause such severe dehydration, such severe electrolyte deficiency that you are put into unfathomable convulsions of pain is laughable. It would be remiss not to be derisory in response.
Either you have some other condition for which mild exercise has revealed these symptoms, or you rode harder than you can handle.
Drink more water, regardless of thirst?
Nonsense.
Oral rehydrant?
You rode too hard, end of story.
I do it too occasionally and pay a similar price.