Jolt.

With the side of her forehead pressed against the cool outer glass she stared out onto the frozen streets. Her breathe streamed a little to the side when she blew out all the spent air, it locally fogged up the window.
The seats were hard. Each manhole cover jarred the bus and she shifted in her seat. Left cheek, right cheek, both, never keeping all her weight on one. Last time she had sat flat on her butt like any normal person would do, but this time was an experiment, to keep her but from getting sore.
Every two or three minutes she would try to hold her breathe as long as possible. A minute and a half was all she had lasted so far, heaving out the air onto the window where it would obscure the view. Half a minute was weak, she could do better.
There was no point in bringing a book to read. The bus ride made her so nauseous, with the back of her throat twitching, that reading would lead to a most violent upchuck on the hard plastic seats.
There was that cold sweat, with the recirculating air of the bus staying stifling, hot but never reaching the inner confines of her clothes. It just heated the air she breathed out and blew it back down on her to breathe in again.
The headphones were the protection from older women, bored from the ride, who would try to talk to her if she took them off. It wasn't like she looked particularly friendly, but they were drawn to her, little moths that smelled like cheap perfume to her consuming flame. There was no eye contact on the bus, no friendliness, she just kept within her head nursing empty thoughts.
"Why is the sky blue?" I can't remember, I learned that back in freshman year of high school, but it's gone now.
Each jolt of the bus knocked her head off the window, but it would then return with a dull thunk.
She practiced holding her breathe again. Half a minute really was weak.