First of all, gobby - ****hugs****
i know that can't fix anything, but it helps a teeny bit.
You have a lot going on right now, even someone without depression would feel overwhelmed with grief and anxiety, so first off, your reactions to everything going on are normal... Just remember that...
I know it's easier said than done, but try to find some time every day to write down all the good things that are going on. You have a loving husband that is there for you, your sister is still alive, she may be different, but she is still here... You have "something" on your brain stem - that is scary, but hopefully you caught it early and can do something about it... (that is a good thing, I think.. It would have been worse if you didn't know about it)...
I lost my grampa last year, I know it is hard... While we weren't as close as we would have been (he lived in massachusetts, I live in missouri), the loss is still hard...
I have found when things are so overwhelming I can't even talk about them - I write about them.... I'd take 30-45 minutes or so and just write everything down that i'm feeling... It really helps...
Email me if you like.. I'm here.
good luck,
--stlsinglemomma