My Cat Just Went NUTS?! Food Aggression?! Help!

I have two cats; Ursula (a little over a year) and Buffy (just under a year).  Both are spayed females.  Lately, Ursula has not been wanting to play, and has been more aggressive toward (but still mostly friendly with).  Recently, the vet gave her some special wet food for indigestion.  Ursula went crazy... growled while she ate, grabbed it out of the bowl, hid while she was eating.  Since then, she has been a lot more excited to get fed and desperate for her treats.  But today she went INSANE!  We got Chinese delivered and she was clearly all about getting it... Because I felt that eating and not giving her anything was unfair to her, I gave the cats dinner half an hour early.  Ursula growled while she ate.  She has never growled eating dry food before.  Shortly after, I took an empty carry-out container away from her and she swatted and hissed at me.  This would not seem weird except she's LITERALLY NEVER hissed at me since we got her at a few weeks old.

Then she dug some leftover onion rings out of our trash can and held it in her mouth, growling at Buffy (who showed not an ounce of interest in the onion ring) and when I went in there to check on the growling, she went nuts.  She ran into the living room, under the couch, back into the kitchen, and into the back of the pantry, where she sat howling and growling and spitting.  I tried to nudge a treat over to her to see if she was even "open to negotiations" and she hissed and spat it, attacked it, and swatted it away from her.  After she finished the onion ring and the treat that was still on the floor, it was like she was almost back to normal.  During this process, she drew blood from me twice.  Is this food aggression?  Could she be sick?  Should I take her to the vet or just be as vigilant as I can be in regards to food?  Right now her diet is a half cup daily of Wellness Core Indoor cat food, which she loves.  The half cup a day is what our vet recommends.

I have never, ever seen her act like this.   I kind of want to think that it might just be food aggression, except her refusal to play and her increased aggression towards our other cat.  (For the record, the two have almost always gotten along.  It only took them about two weeks to warm up to each other, nap together, groom each other, etc.)

Please leave advice or any kind of feedback you have!  It was really scary to see/hear her like that, and I am really worried about her...

I am a new cat owner and only know onions are bad for cats.  You may want to check with your vet right away.

That is bad news, and exactly what I was afraid of when I was trying to get it away from her with the treats.

I thought of another factor last night: We moved about a month ago, and I took their sentry collars off a few days ago (they had been put on just before the move, so they should have been worn out.)  Could they just now be starting to feel the absence of the sentry collars and feeling more of the stress of moving, unpacking, etc?

This morning, Ursula didn't beg for her breakfast (so maybe she's not food aggressive?) but is being much more aloof than normal...

How is Ursula doing?  the web says 3-4 days before symptoms from onions appear.  

When did this start? After the new food or before? Is she doing alright now? For some reason she seems to be acting like shes starved, does your other kitty eat her food? Also a half cup really isn't a lot, but how big is she? You might try spliting her daily ration into at least two meals. I feed all of mine twice daily as they get hungry.

She seems to be doing okay... she has calmed down a little but I don't think she's lethargic, because I have been able to get her to play a little. I have not found anything suspicious in the litter box.

This did start right after the new food. Right now she is doing a little better, but still very desperate for any and all food. She does kind of act like she's starved, but Buffy doesn't steal Ursula's food... Ursula is more likely to steal hers. She is around 8 pounds, and I feed them their food in 3 meals throughout the day. I agree that half a cup isn't much, but the vet says Wellness Core food is so packed with protein and the other things cats need, that they shouldn't need as much as they would with some other food...?

I found online that they think "eating disorders" in cats can be caused by stress, and we did just move to this house a month ago, although until this happened, she seemed to be adjusting really, really well. What are the odds she just suddenly got stressed out vs the special food making her... insane?

Try feeding her the food you were feeding before and see if she calms down. I did receive a bag of the Wellness Core once and my cats always acted starved on it. I'm not sure what they put in it, it makes them want it badly. I now feed only canned or raw as I think its better for them. Here's a link to the website I get my recipe  from. www.catinfo.org

Another thing that might help, considering you moved and everything, is getting a feli-way diffuser and see if that helps.

This is the kind I fed, http://www.chewy.com/cat/wellness-c...mulxQh-49leIEEvKU1kNO5i-eBBozzF540aAguZ8P8HAQ

Oh, I should have been more clear: She is on her old food now, because the special food was just for some stomach problem she had. The problem started on her special wet food from the vet, but has continued when I put her back on the normal food (the Wellness).

I have been considering a raw food diet for them, because I have heard it was better for them, but the site I keep getting referred to says "it's better; there are lots of recipes online!" but doesn't GIVE me a recipe... and I don't want to just find some random recipe from a source I'm not sure I can trust. Plus, with the move and everything, we are kind of limited on our resources for the time being so it's a kind of in-the-future type thought... Then I was afraid that it might make this worse for some reason... but maybe if it meant I could feed them a little more than I do now, it would be worth it.

I looked at the Feliway (don't think I spelled that right) but the only kind I can find in our are is the kind that plugs in, and since that would be limited to an area, I got them some sentry collars to try. But I only put them on a couple days ago, so I'm not sure when/if to see results... It just seems like there are a LOT of variables between her vet food/normal food, the move, etc... Do you think the Sentry collar will help?

It might help. I feed my cats canned food and raw. I use http://www.catinfo.org/?link=makingcatfood as its written by Dr. Pierson and my cats have done very well on it. I've noticed mine stay fuller longer and the litterbox is not as smelly.

So how are things going?

Well, nothing like the onion ring incident has happened again, although she is noticeably more aggressive and hostile if there is food anywhere in the room, even if it's something she doesn't like, and growls when she eats.  I'm not sure what to do other than to just make sure we don't leave food out, but it still makes our meal times miserable.  She'll do more than just beg, she gets up on the table, climbs on our shoulders, and will swat if we pull a plate away from her or push her away.  I'm considering increasing how much food she gets a day, but I'm hesitant to go against the vet's recommended amount of food...