C.J.
I have those days, weeks and MONTHS sometimes. I basically had a mental break down about three weeks before Hurricane Catrina hit. I almost immediately snapped out of my depression thinking "wow, those people have REAL problems, this WILL pass."
I GUTTED my house and donated a carful of stuff and donated as much money as we could afford. This has NOTHING to do with your post but knowing things WILL change and knowing here's someone that has it worse than you kind of resets my thinking and the crabbiness melts away.
Btw, your sister is bat sh!t crazy.