We have to drink extra water on prednisone, it's important to reduce fluid retention. Prednisone changes the way we metabolise things like salt and potassium, retaining salt that we would normally have let go of in urine, and it reduces potassium. So limit salt and increase potassium rich foods like avocado, rockmelon/canteloupe and banana. Electrolyte imbalances can cause dizziness. This is a plain language explanation:
https://wellwisp.com/can-prednisone-cause-dizziness-or-vertigo/