I’ve stayed curled up in my loft. I watch my sister from behind the cover of one of my National Geographic magazines. My stomach churns and clenches like it always does when Ruth is mad.

Mad, though, is sometimes better than the alternative. Mad at least means she’s there inside, that she’s feeling things and functioning okay, and that her medication is allowing her to process feelings, even feelings like anger or frustration. Without the medication, it becomes too much.

I know Ruth packed the medication she takes for her depression, because I checked when she wasn’t looking. Not that I expected her to leave it behind, accidentally or on purpose. But you just can’t be too careful.

One of the worst parts about depression is that it’s not like an outside illness, where you can see the broken bone or the red swollen nose. It’s an inside illness where you have to know the subtle signs.

Which is why I’m not super thrilled about her spending so much time alone in the bathroom.

I clutch my stuffed killer whale to me. I’ve learned to pay close attention to any of Ruth’s signs that I can see because the last thing I want to be is clueless. If I don’t pay attention, I might hurt Ruth in a way I don’t mean to.

Maybe a distraction will help. “It is absolutely the most perfect summer day!” I call down.

“Shut up,” Ruth says.

“Hey,” Eddie calls from the driver’s seat. “Let’s everybody be nice.”

Ruth grips the sleeve of her hoodie in one hand and rolls her eyes. She plugs in her earbuds and twirls her finger around her iPod.

Even though it’s the first day of what should be the most incredible trip ever, today is turning into one of Ruth’s bad days. There are normal bad days, and then there are really bad days. The really bad days are when Ruth falls into what I call The Pit. I know the difference between a normal bad day and The Pit. I know the difference, because I know the signs. At least, some of the visible ones, I hope.

Sign number one: She’s listening to John Williams. That’s not so unusual, except that when Ruth is in The Pit, she feels words like barbed wire. She once told me that sometimes when people speak, it’s like broken glass in her bloodstream. Which means that when she’s in The Pit, even David Bowie and Freddie Mercury—her music gods—are out. She can’t stand the words. So she listens to the Saving Private Ryan soundtrack.