It began today. I noticed it a few hours ago, but I was gone most of the day so it could have been longer. She is moving her belly in and out a lot, and she has black gums (she always has) so I'm not sure about that. She is an indoor cat, and she has been eating and drinking normally until today but I haven't seen her do it in the few hours I've been home.
I use public transportation and won't be able to take her to the vet until tomorrow. Is there anything I can do in the mean time?