It sounds like you are a peace keeper. You empathize with people and want to be the one to save the day. I'm assuming this because I'm the same way. It's so hard for me to let people fail. Even when it's not remotely my responsibility. As far as the coworker who talks constantly about panic attacks....no offense...but that sounds like a lot of attention grabbing. No one at my work knows a thing about my panic attacks. Because I don't want people like you feeling obliged to take over for work I miss. It's my responsibility. It doesn't sound like this person takes responsibility for themselves and wants to push blame on others.

In that case, there is nothing you can do but focus on yourself. Don't run yourself into the ground for this person. It's also not really your place to say anything to them, or your boss.

Good example: This kid was accepted into my department as a phd student this past fall. I hated him at first and assumed it was just personality differences. Now, 2 semesters in, he doesn't do jack either. So, not only is he a total douche, but he doesn't work either. Blames everything on other people. Acts like he is above others and is so much smarter than everyone else but doesn't do ANYTHING! Everyone is mad at him but there isn't much we can do. I refuse to cover for him and haven't said anything to our chair. I just watch him run himself into the ground and, honestly, will be really surprised if he is here in the fall.

You can't keep covering for people who don't take responsibility for themselves because it will affect you.

I see you said you have decided on your course of action. I hope everything works out for the best. My only advice is focus on YOU!!