Pure terror. I managed to hold it off until the last minute, but there it was. Piggybacking into the room on the shoulders of the nurse who arrived to take me to the operating theatre.
I'd done quite well up until then. Apart from a teary moment just before me and the bloke left the house, I was quite calm. There was that faintly sick feeling - the one you get before taking an important test or exam - but it had diminished over the course of the three hours I'd been sat in my pyjamas, waiting in the room at the clinic.
Then there it was, the terror. On like a switch. With the nurse telling me matter of factly to say goodbye to the bloke and his mum, take my glasses and socks off and put my slippers on - we would walk to the operating theatre. Walk?
Everything I had read about the operation I was about to have made me believe that I would be given some sort of chill pill and I would be wheeled there. Every single report said it was so. What a double shock then to be walking, completely lucid, through the hospital towards the surgeon's knife.
When I had to stop to put plastic covers over my feet, and a green shower cap over my hair, my hands would hardly do what I told them. The nurse helped and remarked my skin felt cold.
"I think you're scared," she observed. "You don't need to be - it'll be fine." Easy for her to say.
Through a set of double doors and there it was - the operating table. An ominous looking bed with a thin panel jutting out at a right angle for the arm. My arm. Half way along that - a strap that they would tie to help my veins stand up.
Lethal injection, I thought suddenly, and fought off a manic urge to laugh. My eyes took in a block off three tiny steps leading up to the bed and the blood started to roar in my ears.
For an awful moment I thought I was going to faint or have a panic attack as I stood there gawping like an idiot. Then out of nowhere a friendly voice said in English: "How long have you been in Madrid?"
The anesthetist - he spoke my first language. I wasn't expecting that.
"Four years," I replied, the panic subsiding.
"Are you from London?" He asked.
"No, Durham. it's a place in the north east of England."
"Ah, yes, near Newcastle"
"Wow, you know it?"
"Yes, I know it. I have many friends in Newcastle - it's so important to learn English."
I was so amazed that he knew my home town, I momentarily forgot about the panic attack and what was about to happen. I was having a nice conversation with a Spanish person who had actually heard of my home town. Who actually had friends in Newcastle. That was a first, and I wanted to know more.
But there was no more time. The nurse was back.
"Take everything off," she said, so I did. Wrapped in a blanket I took the three tiny steps up to the table and lay down, sticking my arm out on for the anesthetist to strap in.
Medical staff swarmed around me, sticking things on to my body which would probably measure my vital signs when I was out. I looked up at the lights in the ceiling and the upside down forms of scrub wearing phantoms darting about.
It looks like a film, I thought. The part where the hero's fighting for his life on the operating table and you're seeing what he's seeing. And the sounds are all muffled and it's a bit blurry. It looks like a film.
"Sorry, now you will feel a little prick," said the anesthetist. "It is unavoidable."
"That's OK, I told him. It's perfectly necessary."
"And now you will go to sleep," he told me.
I was glad there was going to be no countdown from 100 for me. I had been worried that in my panicked state I was likely to mess it up, and count in the wrong direction or miss out a number.
Instead all I had to do was say: "Night night."
"Yes, but it's evening, not night, so you should say 'good evening'," corrected the anesthetist.
"You're right. Good evening," I agreed.
Then a sense of euphoria began to wash over me. The panic was gone. The fear obliterated. I didn't really care what happened next.
"Wow, that feels amazing," I said. "Really amazing."
Then there was nothing.
I'd been told that I wouldn't remember anything from the time I was under - I wouldn't dream, or at least I wouldn't remember dreaming. Even so, I'd been secretly hoping for some sort of wild vision, or conversation with god. but there was nothing - just a big black hole that only lasted for a fraction of a second.
One minute I was telling the anesthetist how amazing I felt and the next I heard: "Honey, wake up."
I opened my eyes to see the bloke stood over me, smiling. and behind him, his parents.
Wow, that was quick, I thought immediately, and secondly - wow, I'm back, i didn't die! Because even though I knew it was routine operation with a low level of risk there was still that little voice whispering deviously in my ear: "You might not wake up, you might not come back."
Do you remember the first time you became fully aware that one day you would die? In theory most of us realize that we won't go on forever when we're kids. The death of a family pet or a grandparent puts it into focus. We accept it, because usually it's smoothed over with "Rocky's gone to heaven with all the other dogs who died and he's having a lovely time chasing rabbits in the fields".
But when do we really process it? For me, really I think it was only a few years ago. I was walking down the road on my final stretch of the journey to work with the sun in my eyes and I suddenly thought - One day I will just cease to be. I won't have thoughts, or feelings or memories, I'll just be nothing… forever. And my brain struggled to process that one huge statement. and I had to stop and hold onto a tree while the feeling of total unease passed.
Anyway, it wasn't my time to go. I was back. And as I listened to the bloke tell me the operation had been a complete success and the endometriosis had been minimal - only in one place - I felt the euphoria back again. Only this time it was natural.
I'd been asleep for an hour, and now everything had changed. The unknown was no longer hanging over my head. the relief was total - a blinding white light filling my head.
I was in a lot of pain but it hardly seemed to matter. It would go eventually. I would get better in the end. It was over.
Hours later, as painkillers and antibiotics dripped into my arm we watched a colorful and trippy Japanese Anime film. Then we settled down to try and get some sleep.
"I don't think it's hit us yet, how good this is," said the bloke. "This could have been so bad, but it's all worked out great."
Two nights later, it finally did hit me. I was in my own bed at home with the bloke sleeping beside me. Replaying the whole thing over in my head. Silent tears of gratitude began to snake their way out of the sides of my eyes and run down my face.
It's over. I'm going to be ok. The two phrases played over and over in my head like a mantra before I fell into a deep sleep - my first proper rest since before the operation.