‘We’ve got two issues here that we need to deal with,’ she continues. ‘The episodes of amnesia that you’ve been suffering, and the grief and pain you’re going through as a result of Billy’s disappearance. I’d like to tackle them separately, if that’s okay with you. Starting with the amnesia.’

‘Okay.’

‘You’re a private client,’ she says, resting her elbows on her knees and leaning towards me, ‘so I don’t have access to your medical files but, from what you’ve told me about your visits to the doctor, it seems that the episodes of amnesia you’ve suffered are probably psychological in origin, rather than physical.’

‘Dr Evans thinks they were caused by stress.’

‘Yes,’ she nods. ‘Although I think what you’ve been through is more akin to trauma which has resulted in two episodes of psychogenic amnesia.’

‘Psychogenic? Does that mean I was drugged?’

‘No. It means the condition has a psychological origin rather than a physical one. It’s also known as dissociative amnesia.’

Dissociative amnesia? I repeat the phrase over and over in my head but the words mean nothing to me. I thought I’d feel reassured, to finally receive a diagnosis, but all I feel is panic.

‘Amnesia? But I didn’t hit my head. Oh God, is it –’ a thought occurs to me – ‘is it early onset Alzheimer’s?’

Sonia shakes her head. ‘No, it’s got nothing to do with Alzheimer’s. It’s a psychological condition that typically occurs as a result of a traumatic event – war, abuse or a highly stressful situation.’

‘Can I stop it from happening again? Are there drugs I can get?’

‘Not drugs, no. Although hopefully we’ll be able to prevent you from having any more episodes by treating the root cause. The source of your trauma,’ she adds.

‘Dissociative amnesia.’ I repeat the phrase back at her but it still sounds strange and foreign. ‘I’ve never heard of it.’

‘That’s because it only affects a tiny proportion of the population. There is one well-known sufferer, though. It’s commonly believed that Agatha Christie developed psychogenic amnesia as a result of her mother’s death and her husband’s infidelity. She travelled to a spa hotel in Harrogate and checked in under a different name. She said she was a bereaved mother from South Africa called Teresa Neele.’

‘What happened to her?’

‘Several of the guests at the spa recognized her so the police brought her husband up to Yorkshire to identify her. She returned home and never spoke of it again.’

‘God. How long was she missing for?’

‘Eleven days.’

Eleven days.