About a month ago our domestic cat ran away but luckily we found her a week later. She was very weak and thin. After that incident her personality changed so much! She won't leave my lap and demands attention constantly. She stopped cleaning herself as thoroughly as before, became passive and sluggish. The weirdest and the most upsetting thing is that she used to use her litter box always but now she'll always do IT into our shoes... Is there any hope she'll again become the cat we had known?

In case that matters - she didn't have fleas before and doesn't have them now.
Has she been examined by a vet since she was lost? Something happened to her while she was gone. If she was weak and thin, obviously she wasn't eating and I'm wondering if she developed any liver damage due to that. It doesn't take long for that to happen. I would have her examined if she hasn't been seen and some blood work drawn up.
It was a great stress for her so no surprise her behavior changed this much. She may have got some health issues considering she's passive. I agree with alfinnlay and I hope you'll take her to a vet. If possible don't punish her for what she's doing wrong, she's had enough negative emotions. She needs your love and attention.

Last but not least, is she neutered? If not she may be pregnant.
Agree with the girls and I hope she's better now. Let us know, we like updates Emotion: smile
oh gosh, I didn't think of that. I too hope she isn't pregnant, especially if she's so thin. I would like to know how she's doing also. Please let us know. Emotion: smile
Hello again!

She's neutered yes (thank god!) and good news - she was better this weekend! Emotion: smile More active and more lively overall. I hope this change will persist.
Her appetite has been fine ever since we found her so I didn't consider major health problems to be honest. Now her weight is the same as before we lost her. My only guess was a strong psychological trauma but I don't know how much time cats need to fully recover from something like that if they ever can.
Has she seen the vet though since she's been back? Just wondering if there's something underlying going on. I'd at least have some blood work done. How long has it been since her last visit?