The door to the room opens. A man enters the room. He is a Black man, bald and overweight. He is dressed in uniform. Blue uniform, a blue lanyard that reads “NHS”. But I know Steve, the leader of the organisation that introduced me to magic, is a magician. I know he can appear in disguise.

I approach the man and try to kiss him.

He does not let me kiss him. Then no. It is not Steve.

The man has brought me a plate of toast. He has brought me a cup of tea. I add sugar to the tea, which I would never have done in my former life, but a spoonful of sugar helps the medicine go down!

I do not eat the toast. I drink the tea. I am alone in the room again and I urinate into the cup and drink that too.

I am a Ritual Master. And this, drinking my own urine, is a powerful ritual. This is all I need now to survive. It is the most potent of potions I can drink. I am a self-contained, utterly self-sufficient being. I will never need to eat again. I survive on liquids and air and light.

I decide to explore outside the room. Outside my sanctuary. He has not come. So maybe I need to go searching for him …

Time jumps. I am in a corridor lit by overhead strip lights. The electric light is pale yellow in tone. I am sat on one of three chairs in a row against the wall. The chairs are purple, curved plastic. I am still waiting for him to appear.

There are two doors in front of me. One is the door to the blue room with the blue sofa and chair. Behind the other door is an office of some kind, and there is a woman in there, shuffling papers and talking on the phone.

The woman comes out of the office. She is holding out my phone. My only possession ​now – the one artefact from my previous life. There is someone she wants me to speak to.

Him.

When I hold the phone to my ear, I hear a voice I recognise.

But the voice belongs to my mother.

“Hannah?” she says. “Where are you? What’s going on?”

There is distress in her voice. Her voice is trembling with pain and anxiety.

I do not want to hear it.

This is a test. A horrible test, certainly, but one that I can pass. They are trying to tempt me back into the human. They are trying to lure me back into the past.

I hang up the phone.

But, after a moment, it starts to ring. The word Mum lights up the screen.

“Talk to her,” says the woman.

I answer the call.

My mother sounds different now. Calmer. She asks again what’s going on but gently, even cheerfully. I tell her everything’s OK. That I’m fine. I tell her not to worry. I’m in a good place.

This is the last time I will ever hear her voice, I think. This is the way I say goodbye.

They tell me I am being sectioned.

The words jar with my beliefs.

“Section 2 … the Mental Health Act … 28 days … right to appeal … ”

I cock my head.

This does not fit at all. It does not fit in the world of Steve, of Ritual Master, of Shambhala and the invention of magic.

I am not concerned. I am concerned only with the energy I can feel spiralling up through my body and the voices I can hear in my head.

I pace the hospital corridors, delivering a tearful monologue, delivering the greatest performance of my life. A phrase comes to me. The Girl With All the Gifts. The title of a post-apocalyptic horror film released in 2016, starring Gemma Arterton.

I am a magician. I am an actress. I am a writer. I have superhuman strength. I can fly. Anything that can be imagined, I can perform it. Every skill and every ability is mine.

The film came out as a warning, and a prophecy.

And because of me, the apocalypse has been averted.

I am the saviour of the planet. I am the girl with all the gifts.

It was very hard, the journey to get here. It took 27 years. The path was twisting and full of setbacks, there were challenges and so much pain. There were  times I wanted to give up. It was very hard. Everyone will have to make their own journey, and their journeys will be their own, unique as snowflakes or fingerprints. That is the beauty of it, the joy of it. Everyone has to figure it out for themselves.

But I have laid the groundwork. I have walked the path. It starts with the energy healing, and it goes on and on through the seven dimensions, through increasingly magical planes. It goes on and on until you meet your soulmate, like I met mine.

I was in a TV show called Game of Thrones, hidden in plain sight in the midst of a cultural phenomenon. I, the key to the world’s salvation, wore the face of a character called Gilly, but really I played every role. Then I worked on a film called Detroit in Boston. David Benioff and Dan Weiss and Kathryn Bigelow were the four horsemen of the apocalypse. Numbers are irrelevant. Three counts as four. David and Dan and Kathryn cast me in the roles that brought about my destiny. The end and beginning of the world.

I am the Ur-actress. I am every actress. Every performance ever given has been animated by my energy, my talent, by the gestures and facial expressions I am performing here and now.

This is an edited extract from The Make-Believe: A Memoir of Magic and Madness by Hannah Murray, published by Cornerstone (£18.99). To support the Guardian, order your copy at guardianbookshop.com. Delivery charges may apply.

Hannah Murray will be in conversation with Jessie Cave at Kings Place in London on 5 June.

Top image: Murray wears blazer, by Marina Rinaldi; trousers, by River Island; top, by Phase Eight