We have four cats - 7, 5, 3 and 1. All rescue or stray. The elder two Bustopher and Mungo (male) were both stray and just moved in 4-5 years ago. Very friendly (with us, not generally other people). Mungo dotes on Bustopher. Teaza (3, female) was born in a rescue centre, 5 months old when she came here 3 years ago. Lena (1, female) also rescued, was different. Living rough (pregnant at 4-6 months), was picked up by the rescue centre, had 5 kittens, all now rehomed, then came to us at just under 1, 3-4 months ago. Very nervous at the start, is now friendly and likes playing with us and the other cats - or did until three days ago. We have now had three cat fights involving Lena, the latest an hour ago, and what happened then was typical: Lena is tiny and Mungo is a big cat - but a wimp. She was playing with Mungo, lying on her back waving her paws at him, he was playfully prodding her. He saw an opening and playfully jumped on her. She totally flipped and went into full attack mode - no play at all. She chased him all around the house before we could separate them, trying bite and scratch him. They are now separated, he is very subdued, she is back to normal and wants to play again. The other two are a bit twitched. This is the third time in three days. For the previous 3-4 months they have got on fine, now this. We are at a bit of a loss. Lena at some point, before we knew her, had a very nasty injury near her eye which led to an abcess and scar. Whether related to that or not, it seems that something triggers some old bad event in her life a bit like PTSD does, she flips and changes totally. Then changes back again. Any suggestions on how to address this would be welcome, as permanent separation is undesirable and difficult. We have Feliway in place, but are pretty stumped on what to do to change this. STOP PRESS: Mungo just got through a door by mistake, was walking quietly towards another door, Lena saw him and flew at him.