Bill nearly drowned when she was a kid.
It wasn't dramatic. There were no Baywatch-style lifeguards rushing to the rescue as she photogenically sank beneath the waves on a beautiful beach.
She was eight and swimming in the big pool for the first time, the pool where the water was nothing like being in a bath because it was colder, it was twenty-five metres long and, most importantly, the deep end was twelve feet deep. Bill had been itching to get out of the kid's pool for months, because everyone knew only babies swam there and all her friends had been allowed in the big pool ages ago.
All her friends had started swimming when they were toddlers. What with one thing and another, Bill didn't get into a pool for the first time until she was six, and even then, it was only for lessons. Moira didn't like swimming and you couldn't go to the pool if you didn't have a mum in the water with you.
But then Bill turned eight and she went swimming with her friends and a couple of their mums for someone's birthday, and none of them swam in the kiddie pool anymore. She was fine when they were messing about at the shallow end. That wasn't any deeper than the deepest bit of the children's pool, and Bill could swim from side to side and even put her head under the water, no problem.
Then they started swimming the length of the pool because Amy Hyde declared they had to race, and Bill was no chicken. She wasn't the best swimmer, but she had her ten metres badge and how could twenty-five metres be any harder?
The problem wasn't the distance. She didn't get tired or anything, no matter what Crystal said.
The problem was that she suddenly realised she couldn't touch the bottom of the pool. Not just couldn't touch, the bottom was so far away and she could sink and never reach it and the sides were so far away and Bill tried not to panic she really did but it was all too much and the water was so deep and--
She started flailing. Flailing led to water splashing over her head and going in her mouth. That led to choking, which led to more flailing, and then she was breathing in water and sinking and she forgot all about her swimming lessons...
A lifeguard pulled her out. Bill didn't remember what he looked like. All she remembered was sitting on the bench wrapped in a towel, coughing and shivering and feeling like she wanted to throw up.
Amy Hyde kept going on and on about the hot lifeguard and how special it must have felt when he rescued Bill. Amy's older sister was boy crazy and Amy wanted to do whatever her sister did, even if she really didn't get what it meant.
Bill didn't feel special. She felt small and confused and embarrassed. She kept going to swimming lessons, but it was a long time before she went swimming with her friends again.
Almost suffocating in the vacuum of space is nothing like drowning and exactly the same.
After the high from outwitting the company and saving what was left of their workers wore off, she plastered on her brightest smile until she could escape from the Doctor's office. Inside, she was small and confused and shivering again.
She thought about going back to the swimming pool, for about two seconds until she remembered it had closed years ago and, anyway, that was the kind of morbid thing people only did on TV shows like Casualty. Right before they fell in the pool and got electrocuted or something. So she went home. Not to the grotty house she shared with Shireen and the others. Home.
Moira was out, but that was fine. Bill didn't want to answer questions. She wanted to curl up on her bed and hug her knees until the shivering wore off. She wanted to stare at the damp patch on the wall that they'd never got around to fixing. She wanted to just be, for a while, until the sick feeling went away and she felt normal again.
This wasn't something the Doctor would understand, she knew that instinctively. And he seemed to be brooding over something, which wasn't what she needed. He'd try to be sympathetic, but there would be that puzzled look in his eyes that he got whenever she did something too human that he didn't get.
He was two thousand years old. She bet Time Lords didn't have to worry about drowning. Apparently they didn't even need to worry about suffocating in the vacuum of space. Bit of blindness, quick zap with a red laser and it all got better, no problem.
Bill had never thought that she could die on one of these adventures, not really. Not deep down where the scared little girl who nearly downed in a swimming pool still lurked.
So she sat on her old bed and shivered and shook, waiting for the horror to fade. Reminding herself she could breathe, that the air was safe and plentiful and she didn't have to be afraid right now.
Because that was the part of almost drowning that was a bit like almost suffocating: after a while, it gets better. And you go back in the pool, or the TARDIS, and you know what to do now when the air gets thin and the water tries to pull you down. You know there's a lifeguard or a Doctor who will catch you, and that thought chased some of the fear away and Bill felt better.
Bill felt ready for the next adventure.