I sleep on the futon, usually hedged in by cats, of course.

Okay. Here's an interesting situation.

My second and third fosters were a pair, and as I tend to see in pairs, one
of them was far more aggressive (not in a bad way), and the other was very
submissive, very thin, and a little older. I took them because they were
surrendered, not eating, and starting to develop URI.

They went back when they got better, then we ran out of cage space so I took
them back. During this stay, the aggressive cat turned aggressive in a bad
way. She attacked -both- of my owned cats, the dominant one twice, and even
punctured her in the back, by her hips. I had to separate them in the
apartment. Eventually, cages opened up and they went back again. This time,
shortly after they went back, they were separated from each other because
the dominant cat was bullying (hissing, growling, and swiping) the
submissive cat. Shortly after that, she bit a human. After her quarantine,
she was euthanised because she's proven that she is quite aggressive (which
I can explain, if anyone wants me to).

The submissive cat, however, blossomed. She gained weight, came out of her
shell. The problem? Now SHE's becoming aggressive. She was, if not highly
affectionate, highly tolerant of my cats. She was supposed to be moved into
the multiple cat room, but she was hissing at the other cats just going by
cages. I brought her home again (she's the new, not-new foster), and she's
relaxed enough to climb in my lap and wander around and eat and all, but
I've already caught her stalking the male I'm fostering, and she's swatted
the little female, and hissed at both of mine.

I can't help but think that she's determined to do the bullying so as not to
be bullied again, but does anyone else have any ideas as to why a timid,
sweet, social lapcat would turn into a cranky old bat within a couple of
weeks?