My Mum In Hospital For AF, In Sinus Rhythm Now,

My Mum in hospital for AF, in Sinus rhythm now, she's drowsy and talks like she,s drunk, could be her loose dentures ! Her potassium levels went up yesterday, ok today, I'm concerned about side effects of the Metopronol she's having. Currently she's on 25 mg 3 x a day, I don't like these nasty drugs which have worrying side effects like cardiac or respiratory arrest and death !! What about Vit C as an alternative ? Or Magnesium ?