Does she need an x-ray?

Villy has been having some problems with her back legs. Occasionally, she looks very stiff, and won't put weight on her left hind leg properly. She'll hop around for maybe 15, 20 minutes, then she'll be fine again. This has happened twice that I know of.
I took her to the vets, and they felt her hips and legs but couldn't tell what was wrong. They recommended that I bring her in for an x-ray.
Not only is this going to cost me a lot of money (I do have insurance but still have to pay the excess, which is around £120 because of her age),
but it is very stressfull for Villy. She will have to be starved from the night before, she will have to spend a day at the vets, she'll have an anasthetic, blood tests etc.
She's booked to go in tomorrow, but I'm wondering if this is absolutely necessary? I guess it's the only way to know for sure what's wrong, I just don't want to put her under stress without good reason.
She had a steroid injection a couple of weeks ago for an ulcer on her lip, and she has a food suppliment for the arthritis in her shoulder, so she shouldn't be in any pain theoretically.
I'm also pretty scared that it's something serious.
What do you think? Does she need the x-ray? What could be causing this? At the moment she's an indoor cat.

For what you are saying, I do think the x-ray is necessary... I hope it is nothing serious...

I would agree, hopefully it will be enough to catch what is wrong. If it's a nerve problem, they may not find anything.

My worry would be that a) she might begin to have more problems walking and b) will this eventually affect her ability to properly pass bowel movements and urinate.
So yes, were it one of my cats whether the x-ray was needed wouldn't be a question.

My 14 y/o cat just had a dentistry last week and they also did an x-ray and found LOADS of arthritis in her spine. I was worried about her being there all day and the anesthesia and I felt awful about leaving her, but she did great with everything and was back to normal in no time. The x-ray sounds necessary for her, at least to rule things out if not tell you what the cause is. Hope it goes well!

Have they done blood work as well? If not, I'd ask for that, too.

Hi everyone, thanks for your help and support.
Villy has had some bloodwork, everything is fine.
They've done the x-rays, she's just coming round now. They x-rays didn't show anything, which, although it's frustrating that we don't know what's causing it, is great that there's nothing wrong, no arthritis. Although, it could be really early arthritis, as that doesn't show up in x-rays apparently.
The vets wanted me to give her metacam, but I've heard that can have terrible side effects, and she has had a bad reaction to it in the past (ulcers on her lip), so I said this to the vet, and as she's not stiff all the time at the moment she doesn't have to have it. phew.
So what could it be? I have to keep an eye on her and take her back in two weeks. I'll see how she goes.

Did u think of luxation of the patella..its not common in cats but it does happen...sounds like the symptoms fit ?

Honestly, my first thought was Calicivirus. I found this site a few days ago when researching something else.

http://www.peteducation.com/article....1+1348&aid=210

However, if the vet drew blood, I would think this would show up.