which would be more serious "atrial or ventricular fibrillation" and why ?

Answer 1

ventricular fibrillation, because when you're in v-fib, you are pretty much dead unless they can shock your heart back into rhythm. With atrial fibrillation, it can be treated with anti-arrhythmic drugs.

Answer 2

If u don't take care of ur self and take the needed medication
even a fever will be fatal. So take the prescribed medicine and follow the diet regime told