She keeps busy on day 1.
During those long, never-ending hours when the plane is missing and no one knows anything, she pretty much lives at the hospital, because if she doesn't stop moving, maybe she won't think. She doesn't sleep, she barely eats, she helps out in the ER and where she can, she babysits Zola for a few hours. When she's not working, she stays near the phone in her office or at the nurse's station, because it could ring at any moment, telling her that they – because there are other people she cares about on that plane too, even if her brain is too busy worrying about one of them in particular to spare a thought for the others – have been found all alive and well, and that the whole thing has just been a giant misunderstanding. Her heart stops beating every time she gets a page, or every time she sees Owen, and her stomach is nothing but a ball of nerves.
She decides that he cannot be dead on day 2.
Because if he is, then the last thing her best friend would have heard from her is that he had to leave her alone, and this cannot happen. She can't remember the last words she's ever said to Reed, and she refuses to acknowledge "I don't need your pity" and "leave me alone" as the last things she said to Jackson. To acknowledge that the last time she saw her best friend, she pushed him away as he was just trying to take care of her, like he always does.
Oddly enough, she doesn't cry. She's known to be the emotional one, she's pretty sure every one of her co-workers has seen her cry at some point or another, but she's feeling too terrified to shed a tear. The only time she comes close is when she hears Catherine Avery yell at Richard and Owen and demand they do something, but her mentor's anger only reinforce her belief that Jackson will be fine, because there's no Catherine without Jackson, and Catherine is here. Well, Catherine is here, but she's also not, because the broken look in her eyes when she meets April in a corridor and falls into her arms is very un-Catherine-like. And still, April doesn't cry.
Mark Sloan, of all people, forces her to go lay down in an on-call room on day 3.
She doesn't have the energy to refuse, and if she had, the look on the attending's face would stop her. It's fear, it's weariness, it's guilt for sending Jackson in his place, for making him take his spot on the surgery team as a parting gift, a reward for passing his boards. It's full of all the things he hasn't said to Lexie, and all the things he hopes to say to her one day, and before he leaves, she squeezes his hand, because she knows all too well what he's feeling.
She tries to close her eyes, but opens them right away, because of course she sees his face. His face laughing after a corny joke and too many beers at Joe's, his face frowning as he's trying to find the answer to one of her questions during one of their many study sessions, his face softening as he looks up at her, at all of her, in a hotel room in San Francisco. She doesn't know how she manages to fall asleep, but she wakes up with the covers lying on the floor and her scrubs all sweaty. She doesn't remember having nightmares, but then, she's living through one.
Alex yells at her on day 4.
They're in a patient room, doing some last check-ups before discharging him, and he starts yelling for the most insignificant reason. She yells right back at him, right in front of the patient too, before Richard comes into the room and asks them to leave the hospital and go back to their place to get some rest. He says he'll call them as soon as they have some news, and Alex mutters "whatever" and leaves without waiting for her. She's tempted to ignore Richard's order (he's no longer her boss anyway), but then she sees Callie pacing in the attending's lounge, clutching to Sofia, and Mark, his head in his hands, and Owen, who has maybe said three words ever since they found out, and she goes home. At the apartment, she goes straight to Jackson's room, snuggling under the covers in his bed, and only moves when Alex gruffly tells her that the food he ordered just got here. He ignores her when she says "thank you", and they eat in silence.
The phone rings and her pager beeps on day 5.
Alex drives like a maniac while she bites her nails in the passenger seat. She's tried praying the past few days, but the lines of communication between her and God are a bit murky at the moment, and it only makes her think about all of her failures, which makes her think of how she made Jackson feel responsible for them, which turns her stomach. She still manages to send a quick prayer, mumbling under her breath, not knowing if it'll be heard, and Alex doesn't even make fun of her.
At the hospital, they run, don't walk, straight to the conference's room, where most of the attendings are gathered. She can see the tears on Mark Sloan's face, and her heart stops.
It starts beating again when Hunt tells her that there was only one casualty from the plane crash, and that Sloan is weeping for someone else than his protege. The shock of hearing Lexie is dead battles with her relief that Jackson is alive, the two concepts clashing and jarring, and that's when the tears finally come. She finds a wall and slides down to a sitting position, her body racked with sobs, and Bailey kneels next to her and softly repeats that Jackson is okay, thinking she's misunderstood what she has just heard.
Jackson (and all of the other survivors) comes back on day 6, and a new kind of waiting begins.