I'm a bit concerned about Candy

Hi all I have a bit of a problem with Candy, she is 7 and as some of you may know we moved house recently, all the cats have settled in really well and also adjusted to our new cat Harvey well. I thought also Candy had settled in well but this past week she has been acting very odd, every time anyone walks past her she growls at you and attacks you. She comes out in the garden when we are out there and we were sittin outside last night and she came out, all of a sudden she spotted her own tail moving and growled at it and ran off down the garden.
This really is worrying me as she has never done anythin like this before, about 2 years ago I took her to the vets as I was worried about her as she was havin lack of co ordination and kept twitching, she is extremely small for her age and also she sits strangely. After he examined her he said that her facial features and some of her traits he said were linked with what he could of thought as a feline equivalent to Downs syndrome. I asked him for further tests and advice and he said there isn't much info available over here and also not really a definite diagnosis "test" and he could not really help me any further as it should not affect her life.She has regular heart check ups and has to have flea allergy shots.
I do not know if this recent behaviour is linked to this or us moving. She pretty much stays on her own and doesn't have alot to do with any of the other cats, I just wondered if anyone had any advice or has witnessed anything similar.Thanks.x

Thankyou, I shall phone the vets in the morning, she has always been a bit grumpy but nothing like this, its quite awful to see. All the other cats are happy here and I feel like I have let her down if she is unhappy here. x

There are alot of stray cats around here, one in particular that is bit of a bully and has tried to go for smartie but as they are normally just out when we are I know Candy hasn't been bullied by this cat and I have been shooing it away when I see it and the last couple of days I haven't seen it much so I am hoping that it has got the message that it isn't welcome. Could this be causing the problem or maybe some of it do you think? It does spray in our garden, its an unneutured male. I of course will still ring the vets in the morning and get her in. x

Well, all is ok and she has been given a clear bill of health. I'm not sure what bloods he did but all have come back ok. The vet said he thought it was a stress problem and recommended feliway. We have only been here just over 3 weeks and I suppose it is early days, she wasn't too bad today just the odd growl here and there. Its possible that she is finding it hard to come to terms with Harvey being here. I will try the feliway and if it fails then back to the vets i think, thankyou for your advice.x

Ooooh, i have Bachs rescue remedy I use it for myself She hasn't been too bad today but I have been keeping her in more, even though the kitties only go in outside when we do generally I have tried to keep her in completely and give her lots of hugs, still quite alot of grumpiness and she keeps spotting her tail wagging behing her and attacking it? Why would she do this? x