It is difficult to come to terms with the knowledge that ones parents are not perfect and going to live for ever Usually that knowledge slowly dawns on us P.D makes us come to that realisation sooner even though it does not significantly alter life expectation.To a certain extent, as a result of living away and your mother's P.D, you have had to face that knowledge suddenly and it has hit you between the eyes and naturally you do not want to face it.That is not selfish just a natural response.Your role has changed as regards your mother:you are no longer the child and your mother the all knowing,protecting adult but she is essentially the same person and you need to get to know her adult to adult.As I lost my mother before I reached my teens my greatest sadness is that I never really knew my mother except through the eyes of a child.You have that chance:PD has not changed the person she is but you can no longer have the invincible woman that you saw as a child but she is the same women.
I have not said you need to grow up what I have said is that you need to come to terms with the fact your relationship with your mother has changed and accept and enjoy it.
You probably do not like what I have said and think I have got it all wrong(I might have done so) but it has been said in order to help and I have thought a long time before posting.