Pieces....
I am sorry for your fear......
I really do think that talking to your mom about your feelings will help, as for your friends, you are allowed to ask for support from them, especially if you are giving them the support they need.

I have lost many dear people in my life, not my mom, but all of my grandparents, especially my grandad, who I was extremely close with (closer than my parents.)
I lost him to a stroke.....
I struggled for a very long time to get "back on top" of things, but the one thing I have learnt, is that even when the ones we love pass, they never truly leave, as long as we remember them.

I know this doesn't help with your fears of your mom passing, I just hope it will make you less fearful.

Flinty