https://www.youtube.com/watch?v=lwmpa5-riAw

13 minute clip. Character is poisoned / drugged and everyone thinks they are insane, and they see dead people briefly.

I would like a Bruce Willis cameo for the Cokers. Les slumps against the wall, cries and whispers to Bruce "I see dead people..."

Peggy Mitchell rises from her grave as a zombie and starts to make her way to the Queen Vic......

It sounds like Belle Dingle in Emmerdale though in her case it's a mental health problem and not drugs/poison.