Unfortunately, you can't speculate on a cat's depression. You can, however, get sufficient information for prescribing just from your observations.
Here's what you reported about the cat:
It pulls hair out of its tail (trichotillomania)
It is overweight (you should be able to feel--but not necessarily see--a cat's ribcage under its fur)
It is unable to clean himself properly
It has lots of flakes and flakey skin (not necessarily a result of an inability to clean itself)
It is responsive when given attention (now you just need to clarify how it responds--does it love being stroked or petted? Does it like this for quite some time, or does it react from overstimulation--by eventually biting or scratching in response?)
You can ask the cat's human family members to give you more information--does the cat have any fears? Does it have a favourite place or activity? How does it feel about other animals, particular people in the household? Does it crave any particular kinds of foods above all others? Does it like company? Does it prefer to be alone? How does it respond in each respective situation?
There are plenty of things you could do to promote a healthier, raw food/natural food diet for the cat, and perhaps find some ways to educate the human companions about fleas (if there are none around on the property and none in the house, those monthly program shots or treatments are just harming the kitty and making the vet wealthy...) In my experience, animals become susceptible to fleas and other parasites when they undergo some kind of traumatic emotional experience, such as a kind of abandonment which causes them anxiety. Otherwise, they don't fall prey. So, it is very important you look for some kind of etiological evidence--find out when the cat started biting out its fur, when it started to put on weight...
The cat's food intake should be severely restricted until the excess weight is lost, however; and that can be done with natural foods more easily than it can be done with commercial foods (as the ingredients can be controlled more easily). Find out why the cat won't go out of its garden environment (is it frightened of what's out there? If so, that's another symptom to repertorize) and see if you can encourage a bit of exercise with cat toys if that's at all possible (which means the human family members have to put in some time with the kitty--that could be telling in terms of rubrics for you, too).
Richard Pitcairn and his wife have published all kinds of natural food recipes for cats that you may be able to find on-line. You might want to try this site, too:
www.blakkatz.com for more information on natural food diets and homeopathy for cats.
Good luck!
[ 24. August 2002, 14:32: Message edited by: ChaChaHeels ]