Veterinary questions? Ask a Vet for Answers ASAP
Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you today.
For Izzy to come in looking stressed and painful with her back leg suggests either a injury. It could be from having a fit somewhere outside, a cat fight or road traffic accident. Though with your mention of her jumping being fine, I suspect she has not been hit by a car. If it was another cat, it could be we have a small wound that could lead to an abscess. And if she did have a fit, unfortunately only she could tell us.
In any case, keep her in for now and monitor. As she calms, we want that breathing rate to normalize (~20-30 breaths per minute) and her gums to be as pink as usual. If that is not the case or she seems very sore, then we'd want a local vet to see her since there are no safe OTC human pain relief options we can use in cats (all are toxic to them). But it sounds like she will settle here and you need just keep an eye. Though just to note in case you were keen to have your wee one seen today, some vets in our country have office hours today. As well, I wanted to mention that most practices have contingency plans for emergency care for their patients even when they are closed. Therefore, it is worth ringing the practice. If they are open, you can get in today. If they aren't, then they will likely have a message to direct you on contacting their out of hours service. And if you don't have a vet, you can find a local one via the RCVS Register (http://findavet.rcvs.org.uk/find-a-vet/) or Vets Now (http://www.vets-now.com/find-an-emergency-vet/) who are open all nights/weekends. In any case, if you wanted to get this checked out sooner then there are options to do so.
You are very welcome, my dear.
That sounds perfect and I am glad to be of help. :)
All the best for you both and be safe,