Faye Wilkes, 41, was sunbathing by the pool when she felt a sharp nip and she swiped a bug off her left foot.
A red mark instantly appeared, but the personal assistant thought nothing of it and spritzed herself with insect repellent to prevent further bites.
It was only when Faye was left unable to walk four days into her girls' trip that she started to worry.
Faye's whole leg swelled up and she claims she got turned away from a hospital in Spain as medics thought she was a 'typical drunk Brit'.
The mum-of-one cut short her break after four days to seek medical help in the UK after her leg blistered and started to become infected.
She was rushed from Gatwick Airport to East Surrey Hospital, where doctors told her she had contracted a flesh-eating infection, likely to be necrotising fasciitis.
It happens when bacteria enters a wound, causing sepsis, and doctors warned she might need to have her leg amputated.
After being pumped with seven different antibiotics and spending more than four months in intensive care, the infection cleared up.
But Faye is still traumatised by the ordeal and is recovering from the holiday nightmare at home.
Faye from Dartford, Kent, said: "We recently lost our dad, Raymond, 66, to lung cancer and to cheer ourselves up, unwind and relax my sister, Carrie, and I booked a holiday.
"We hoped to spend a week soaking up the sun and sipping cocktails, but it turned into a holiday from hell after I was bitten by an insect.
"From the moment my leg began hurting, I knew something was wrong, but I didn't want to waste anybody's time.
"After it started scabbing and I had difficulty walking, I knew I needed to get help, but the Spanish doctors just fobbed me off as another 'British drunk' - I was horrified.
"I trusted my gut instinct and flew home straight away and I'm glad I did, as doctors in the UK said I would have died - or would have at least needed my limb amputated - if I didn't get treatment within 24 hours.
"Although I'm thankful I've been able to keep my leg, I'm still battling with the after affects that this mystery bug has left me, but I'm getting there - slowly but surely."
Faye was on holiday at the seaside resort with her sister, Carrie Wilkes, 43.
Faye had been caring for her dad who was battling lung cancer and heart failure when he passed away in April, 2016.
She thinks she was bitten on the left leg by a spider or mosquito.
Faye said: "I felt like I had been stabbed in my left leg. It instantly began burning up and I thought it was probably just a silly mosquito bite, so I went into the pool to cool it off.
"But as I went in, my leg started to burn up more and my toes began bleeding, which I thought was odd, but dismissed it until the next morning, as I didn't want to waste anybody's time."
After spending her evening walking about she had excruciating pain in her foot so Faye decided to go home early and wait until the next day to seek help.
Faye said: "I woke up in the middle of the night was shooting pain up and down my leg and when I tried to stand up to get to the bathroom, I collapsed on the floor."
After suffering through the night, Faye called a taxi and went straight to hospital for an x-ray.
She said: "I was in so much pain and when the doctor came back to tell me the x-ray looked like I just had a sprained ankle, I was furious.
"I think they thought I was just another British drunk who had fallen over, but even though I told them I hadn't sprained it, they sent me back to the hotel with a pair of crutches."
Faye trusted her gut instinct and left her sister in Benidorm and flew home, but had to be wheeled on to her flight.
She said: "I was too weak to walk on my own and I began being sick every five minutes as I boarded the flight."
Faye begged the cabin crew to phone her an ambulance to pick her up from Gatwick airport when she arrived.
She was admitted to intensive care in Royal Surrey Hospital and diagnosed with sepsis.
Her foot was covered in blisters, and doctors warned they may have to open up her leg and flush out the infection, or if that didn't work - amputate her leg.
She said: "I was absolutely horrified, as I didn't think a measly bite from a bug in Benidorm would result in sepsis, let alone the loss of my leg.
"Luckily, they were able to flush out the infection without having to do any invasive surgery, but I still feel incredibly weak.
"They couldn't find the bug in my system, so were unable to work out which one caused me to have sepsis, but I'm glad that I went to the hospital when I did, as I was close to death."
Doctors told Faye that if hadn't got to the hospital she could have been dead within 24 hours.
She said: "Although they got rid of the infection, my foot and leg is still scarred and my circulation is awful, so I have to keep it propped up near enough 24/7.
"I think it was either a dirty spider or mosquito that brought this pain and distress upon me - but I will never know."
"The main thing is that I'm alive and I still have my left leg and foot - but I know I still have a long way to go until I'm out of the woods.
"I had to learn to walk again and build up my strength."