I feel like the pacing, particularly in the last paragraph is off, which doesn't really leave me feeling swept up in the story or really pack the punch of the cliffhanger.
She turned the tap off and, giving her reflection a final cursory glance, headed for the door. Her bare feet padded silently across the cold stone floor. The distance from the sink to the door was minimal but as her outstretched hand reached for the handle, her legs buckled beneath her and Erika collapsed to her knees with a gasp that was hastily replaced by another wet cough. This time, she didn’t catch it in time and a spattering of red painted the back of the bathroom door. Her eyes widened briefly at the sight. Then she blinked. Again and again. Her vision blurred and her eyes rolled into the back of her head. Then, Erika Hansen lost consciousness.
She turned off the tap and gave her reflection a final cursory glance. Bed. She needed to go back to bed. Cold tiles bit at her feet as she attempted to close the small gap between her and the door.
Her breath slowed as the weight in her limbs increased.
She blinked, the handle gleaming at her from across a room that was suddenly the length of a football field.
A hand as shaky as her breath reached for the door.
And fell directly into nothing.
Knees buckling, she hit the tiles. Hip. Elbow. Shoulder.
Air pushed from her chest on impact - a pitiful moan that ended in a whimper - and it didn't sound like her. This wasn't her.
Another cough. Hacking. Another gasp. Useless.
Her shoulders clenched as she fought for air.
The world darkened, tiles becoming duller, but all she cared about was air.
She lay down, no longer able to carry the weight of her small frame on her elbow. Not when her chest heaved and every muscle in her body grappled with her cough.
Bed. She just needed to go back to bed.
Okay so that's probably not how I'd write a first chapter because it's likely* too much. But if your character is going to faint and almost die, you really need to make the reader feel like that's what's happening. You want them reading quickly (so less big paragraphs - especially the same lengths of paragraphs repeated again and again as that's just an invitation to skim, more small paragraphs, small choppier sentences, white space on the page - subconsciously tells the reader to big up the pace of their reading, dubious grammar etc, because the scene is supposed to feel rushed and a little panicked)... that said, I wouldn't personally do this before the reader was given the chance to connect with the main character. They need to actually care about what happens to her. Right now, we have a teen girl and a brief mention of school and her mother - so basically nothing to differentiate her between any other teenager in the country.
Readers start to care about characters when they feel like living, breathing (coughing 😁) people.
And what makes people, people? Opinions! That's incredibly difficult to do when your very first chapter seems like she's waking up with a bleeding nose?
What makes readers feel like characters are living? Setting! Setting viewed through the eyes of character. Again, not great to try to build any sort of depth with setting when the character is waking up in a familiar surrounding and something has their attention straight away.
IDK. These are just my personal thoughts. It's not a bad piece of writing at all, I could type plenty of great things to say about it too but I don't think that's ever very helpful. So yeah, I'd maybe consider if you could make your job a little easier and start somewhere else. Good luck!