What are these aweful cat sounds?

I have a 1 1/2 year old female cat and a 1 year old male cat. They have been together for about 6 months. They have been known to play rough but tonight I started hearing the older cat hiss. They tussled and since then my older cat has been making these horrible guttural sounds. She went and hid for a short period of time after I put the younger fellow in a separate room. I was able to coax her out with some treats and she did let me pet her but the noises she is making are scary. I don't see any visible wounds or anything but I have never heard sounds like this before. What should I look for? Why could she be so skid-dish? She is not walking around with her tail and back puffed up but rather her tail is down and she seems timid. They are now in the same room and the little guy is quiet but my other gal sounds like she is crying and it is making me nervous. Can anyone offer some guidance, suggestions or help?