What on earth is causing my cat to throw up so damn much?

My 6-ish year old cat has been vomiting just about every night for the last week and a half. It’s almost always pure liquid (brown), and a lot of it. In the past, this was an occasional thing, and there was usually more… substance to the vomit. She seems quite distraught while it’s happening, but is her normal self at all other times. If it doesn’t stop by this weekend, I’ll take her to the vet, but I’m just wondering what could be causing this and if there’s anything I should be doing for her in the meantime?

My other cat isn’t having this problem, but has been sneezing like crazy for the last day or so. Could these issues be related in any way?

Bonus question: Anyone know how to stop her from throwing up on my upholstered furniture? She usually hits the floors (hardwood or vinyl, so no big deal), but the other night managed to puke on the couch, a chair, and an upholstered ottoman. It’s making me a tad crazy.

This one’s for you, bob_.