Associate Professor Ong Thiew Chai, on the stand for a fourth day, said that a person in such a dissociated state could be more vulnerable to being traumatised.

The senior consultant from Tan Tock Seng Hospital was being quizzed on his former patient by defence lawyers seeking to prove that Madam Amutha Valli Krishnan was faking her symptoms to claim damages from the church.

The 52-year-old woman is suing the Redemptorist Order that runs the church, two priests and six church-goers for allegedly forcing an exorcism on her that left her traumatised.

On the stand this week, Prof Ong has stood stoutly by his diagnosis that Madam Valli had suffered post-traumatic stress disorder from the incident in the church.

Yesterday, defence lawyer Tito Isaac took another tack in his questioning: Noting that Madam Valli and her family have focused on the 21/2 hours in the church that August day in 2004, he asked 'to pull back and look at her 25-year relationship with drugs, alcohol and trances' instead.

Pointing to her history of going into trances, he suggested that this was what happened in the church that day. He secured Prof Ong's agreement that it was possible that, while in such a state detached from reality, she could have perceived an event that she found traumatising.

Madam Valli has gone into trances since she was 12. In the late 1980s, she was seen by the entire National University Hospital psychiatric team, including Prof Ong's teacher.

She would slither like a snake, become hysterical and strangle the medical staff.

Mr Isaac noted that her history of doing this was echoed by the defendants who said she crept on the floor like a serpent and was violent.

Mr Isaac, giving an example of a possible 'false memory', said the defendants said that they saw her trying to choke herself, but she recalled being strangled.

He added: 'If my flawed memory tells me I was being strangled by someone when witnesses saw me going for my own neck, that flawed memory can make me feel traumatised.'

Prof Ong agreed this was possible.

He added that Madam Valli was 'very well trained' and was able to enter and emerge from trances at will.