The cobbles businesswoman - played by Alison King – will think she has spotted her late half-brother Aidan Connor (Shayne Ward), Hayley Cropper (Julie Hesmondhalgh) and Rana Habeeb (Bhavna Limbachia), who passed away recently when Carla's factory roof collapsed on top of her, on the Victoria Street fire escape.
Alison said: "She believes she is being watched and followed so in her head she needs to keep on the run, she ends up in the park asking a stranger for help.
"When she won't help her Carla then sees the most beautiful thing that will always help her and that is Hayley in her red coat so she follows her eventually back to Victoria Street and when she can't see her she is absolutely mortified.
"The thing that means the most to her and always helped her get back on the straight and narrow is Hayley and she has gone.
"Then she sees her walking up the fire escape and she follows her - she has a hallucination."
Carla then spots Aidan and Rana - and Alison admits the scenes were "hard to play" because her character was "so terrified".
She said: "The scenes on the fire escape when Peter is there are so emotional, it was hard to play as it was so terrifying for her at that stage, inside her head everything is terrifying.
"She thinks she is seeing Hayley, then she thinks she is seeing Rana and she doesn't know if Rana is dead or alive.
"Then she thinks she sees Aidan, to her it is real, she is in a very dangerous predicament and unrecognisable to Peter who is desperate to rescue her."
I met a beautiful lady through Mind, she came to meet with me at the studios.
Alison was grateful to meet up with a lady from mental health charity Mind who also suffers from psychosis.
She said: "It was really weird trying to encapsulate what she is going through. I met a beautiful lady through Mind, she came to meet with me at the studios.
"When I talked to her I asked so many questions, she suffers from what Carla is suffering and she told me that during those moments of extreme psychosis you are never not yourself but you are just the most terrified version of yourself.
"You are locked in there, when you are spiking in these psychotic episodes there is no way out.
"You are trapped in there and wherever you are or whoever you are with it is terrifying but you need to be free to go through it and this is what I am trying to portray."
Carla's psychotic breakdown will feature in a special episode as her desperation reaches new heights, and Corrie teamed up with Mind to ensure the character's illness has been portrayed as accurately and realistically as possible.
Julia Lamb, who runs Mind's Media Advisory Service, said: "It's refreshing to see Coronation Street explore how traumatic events can lead to psychosis, one of a number of mental health problems which are frequently misunderstood and misrepresented.
"Carla is a well-established, feisty character and her story shows how incredibly vulnerable people experiencing psychosis can be.
"When we worked with Coronation Street to develop her story, it was particularly important not to give Carla generic symptoms but to show it affects her individual character.
"For example, not looking after her appearance or even her diet the way she usually would.
"As well as providing feedback on each script, we also worked with Kerry who met with actress Ali King to talk through how she felt and behaved when she experienced psychosis after a trauma.
"The result is a realistic storyline and a fantastic performance from Ali too."
Coronation Street is on Monday to Friday at 9pm on ITV next week.
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