Here's how Yuna's troubles go in Night Furies vs. The Nightmare Family Part 1.
[the next morning, we see Yuna and Hiccup barely awake]
Yuna: [yawns] Come on, girl. Let's go see how Mama's doing.
[They walk to the kitchen]
Castle Maid: Good Morning Princess Yuna, your dragon's fish is waiting at the kitchen door.
[They head to the counter]
[The Princess Luna comes in as Yuna gives the fish to Nightstar]
Princess Luna: Good Morning, sweetie.
Yuna: Hey, Mama. [yawns]
Princess Luna: Did you sleep well?
Yuna: [almost falls asleep but springs back up] Oh, yeah. Yeah. [yawns]
Princess Luna: Yuna? Are you okay?
Yuna: Sure! Just fine! Thanks for asking.
Princess Luna: [isn't conviced] Okay, then. Well if you need anything, just came find me. Okay?
[As Princess Luna leaves, Nightstar looks at Yuna]
[meanwhile, Hiccup is trying to keep up with things but is too tired to do so]
Astrid: Hey, are you okay?
Hiccup: Ah! Uh, sure I am!
Astrid: [looks at Hiccup for a moument] I don't know, you're hardly keeping up with things.
Hiccup: Oh, don't worry. I'm just fine! [yawns] Come on, bud.
Toothless: [growls in worrieness]
Astrid: [to herself] Hiccup, I know there's something wrong and I intend to find out.
[Later, Yuna and Nightstar come into berk]
Hiccup: Ah Yuna! Come for the daily flight?
Yuna: Yeah. [yawns] I have.
Hiccup: O.. [yawns] okay.
[Nightstar and Toothlees look at each other and then they growl in worriedness]
Hiccup: Alright, let's go.
[they both hop on their dragons and then take off]
[However, Yuna falls asleep while they fly in the sky]
Nightstar: [looks back and moans in worry for Yuna]