I feel so incredibly selfish for feeling the way that I do, but I am scared. I am scared for her, but more selfishly I am concerned for me

I have been having terrible nightmares about her dying and leaving me alone.
I keep thinking that I don't want to go back to therapy next week in case she tells me its bad news (i.e. the lump is cancerous). I know that makes me selfish, making it all about me me me...I just cant seem to stop it.