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Hello. Thanks for the question.
It sounds like she looks pretty bad right now if she's not wanting to get up even after stimulating her. In an older cat with acute vomiting, lethargy and weakness, I would be concerned about metabolic disease. It could be kidney disease, liver disease, pancreatitis or diabetes. These are all common in middle aged to older cats with acute GI signs.
The first step is an exam and baseline bloodwork. The bloodwork will likely point to the organ system involved. From there, she'll likely need to be hospitalized on IV fluids to rehydrate her and then start more specific therapy depending on what is found.
If you can't get in right away, you can try to give an over the counter med to settle her stomach. There are two options- Pepcid (Famotidine) 5 mg orally or Meclizine (Antivert) 12.5 mg orally. I would also try to get some water or Pedialyte into her to help with her hydration.
I hope this helps, let me know if you have any other questions.
I would still try the stomach meds to see if it helps prevent any further vomiting.
If you need to try those at home and see if she starts eating/ drinking, that is ok. If this lethargy goes on for more than 12-24 hours, I really would try to get her seen by someone. I know it's not easy when they're terrified of car rides and the carrier. That's a way to see how sick she really is as well. If she lets you put her in a carrier easily, then you know she's not doing well.
She sounds like a cool cat. I hope the meds get her stomach settled down and she's taking to some food by this afternoon. If she seems to keep declining though, then I would do all you can to get some bloodwork run before they close this evening.