Mary Catherine Derin, 46, from the US state of Maryland, developed Guillain Barré Syndrome (GBS) and suffered a build-up of pressure on the brain — at the exact same time — during the five-day trip.

Ms Derin said she and her husband Tony had only just arrived in Mexico for the holiday to celebrate their wedding anniversary in May 2017 when she started to feel unwell.

On the morning after they arrived, she noticed weakness in her legs and arms and lost feeling in them. By the evening, she could no longer walk without help.

“When I started getting weak and losing feeling in my legs, we thought I was coming down with the flu,” she said.

“We ended up going to the on-site doctor and he thought I was dehydrated, so he gave me IV fluids. When that didn’t help, we knew something was wrong.

“While we were there, I started having spells of blurry vision, but I figured it was just related to getting the flu. I would just have moments when things would go black and then come back blurry.

“By the time we left Mexico I needed full assistance to do everything. So, over the course of five days I went from being able to walk to being completely paralysed from the waist down.”

When the couple got home from Mexico they went to an emergency department where she was diagnosed with GBS — a condition in which the immune system attacks the nerves, leading to rapid onset muscle weakness.

“They treated my GBS, but they couldn’t understand what was causing the problems in my vision,” the business owner said.

“So, after a couple of weeks, I transferred to a new hospital at the start of June. Within a day of being admitted to a new hospital, I was completely and totally blind.”

Doctors discovered the cause of her mystery blindness, which was related to a condition Ms Derin thought she had outgrown as a child.

She was born with hydrocephalus — a build-up of fluid on the brain — and required a shunt when she was a month old. By the time she was five, doctors said she had outgrown the condition and no longer needed a shunt, even though it wasn’t removed.

But the neurosurgeon she saw after the holiday determined Ms Derin did still need her shunt, and it had been malfunctioning and allowing pressure to build up on her optic nerves.

“This led to pressure build-up on the optic nerves, which killed them and led to my vision loss, so I was rushed into surgery and my shunt was replaced,” she said.

“They replaced the shunt in the hopes that the pressure would slowly be released and my vision would return over time.

“In the weeks after my brain surgery, I started getting some vision back and my neck pain ceased. So, while I no longer had pain, I was still blind and had no use of my legs. Throughout this, I was working closely with physical therapy to start gaining mobility and be able to walk.”

Ms Derin spent three months in hospital where she did regular physical therapy to learn how to walk again.

GBS left her with very little mobility and strength, but she learned to walk with a walker before then using a cane.

Six months after surgery, Ms Derin regained some vision, but it was distorted as she didn’t have any depth perception or peripheral vision and she couldn’t distinguish colours, instead seeing only muted browns.

“When I was released, I could use a walker for short distances, but when we went out, I still needed a wheelchair because I got tired very easily,” she said.

“However, within a month of coming home, with extensive rehab and physical therapy, I could walk with just a cane.

“It’s believed that my shunt malfunction and contracting Guillain Barré Syndrome were completely unrelated and just happened at the same time. The doctors said it was an incredibly rare situation.”

Ms Derin said she’s had to learn how to adapt to her “new normal” and keeps followers updated on Instagram.

“I came home from the hospital and I am now legally blind and very weak with poor mobility. So, I had to modify a lot of things I did before,” she said.

“For example, I can no longer drive because of my blindness. Sometimes, I just have to do certain things differently.

“I used to be a fitness instructor, so it’s been very difficult for me to adjust to losing so much strength and no longer having the mobility I had before.

“However, I’m very grateful to have regained a small amount of my vision back and have the ability to walk now, considering that when I was hospitalised, I was completely blind and paralysed from the waist down.

“Life does not offer roadblocks, it offers detours. It’s all in how you look at something — it could always be worse.”