Lightheadedness & major thirst during prep

Hello! I'm currently in the throes of prep, took my first dose of plenvu (500ml) plus 500ml apple juice at 15:30-16:30, then the second at 18:30-19:30.

I've been having major diarrhoea since 17:00 - as it should be. But I also feel lightheaded and super thirsty, which I don't remember from the last time I did prep 3 years ago. Is this normal? I'm drinking as I go, chatgpt says I should sip slowly but I find it hard, I'm so bloody thirsty.

How much extra liquid are you supposed to drink aside from what you drink at the same time as the prep liquid? I can't find guidance about that anywhere.

Also is this lightheadedness normal? Chatgpt says i should drink an electrolyte drink but I don't think I could stomach it after the nauseating flavour of the plenvu prep 🤢