You're thirsty because in AF one does not retaining sodium (I imagine you pee everything you drink out quite quickly, and more so at night?) so you cant retain water - no water, no hydration, increased need for hydration - thirst.
So make up a salt water drink and sip it throughout the day, once you get to saturation level, you'll get exceptionally thirsty, and when you drink, youll feel hydrated.
Continue to do this everyday, dont forget, and salt your foods. Find the amount best for you, I work on 2-3 teaspoons a day, when I crash, I can easily take 3 x that, i barely taste the salt at all.
I actually make my own electrolyte drink up, fresh 250ml of cocount water, 1/2 teaspoon Alive food source vitamin c, a little magnesium citrate with 1-2 teaspoons of added pink salt. Drink throughout the day. If you pee more, its too much potassium for you. Make sure you add the salt as otherwise youll be potassium heavy, which you dont want.