When Anne Curtis started to feel unwell, she put it down to the flu. Her symptoms were at the extreme end of the virus, but she brushed them off as a severe bout.

Even an NHS doctor was unable to spot that she had a potentially deadly case of Sepsis.

"I didn't think much of it but then I started to get worse and there was one day when I was sweating profusely, just normal flu symptoms but they were fairly extreme I thought," Ms Curtis said.

"The doctor didn't pick up on it although the signs were there. He thought it was some kind of flu and I could take paracetamol and feel OK.

"Everybody has different perceptions of pain, and maybe he understood it to be not very much, just flu and nothing to worry about."

Tuesday is World Sepsis Day, which raises awareness of a condition which is still rarely discussed despite it killing around 1800 Scots each year.

The illness can often have the same symptoms to a number of less serious conditions but can result in septic shock, and permanently damage limbs and organs of those who survive.

Previously known as blood poisoning or septicaemia, sepsis is a life-threatening illness that arises when the human body's response to an infection spirals rapidly out of control and makes it injure its own tissues and organs.

Even with intensive medical care, sepsis can quickly lead to shock, multiple organ failure and death.

It remains the primary cause of death from infection despite advances in modern medicine over the last 50 years, including vaccines, antibiotics, and intensive care.

Quick treatment is essential in the battle against sepsis. Evidence suggests that if it is treated aggressively within the first "golden" hour, the risk of death is halved and survival rates can be more than 80%.

For Anne, this was crucial. After returning from the doctor having been reassured that she was alright, her condition rapidly deteriorated overnight, leading her and her husband trying her local doctor for a second opinion.

Luckily he recognised the situation was much more serious. "Things got worse overnight and we thought 'this is something more than just flu', and we went to my local doctor and he immediately looked at my legs which were all swollen and sent us straight to hospital.

"I went to the local hospital and they immediately saw that it was sepsis, and shortly after that I went into septic shock.

Septic shock is a life-threatening condition that is a result of a dangerous drop in blood pressure after an infection.

Anne's life was in considerable danger, and doctors had to battle to stop her from succumbing to the illness.

"They have to save your life because your blood pressure drops and I had an atrial fibrillation (irregular and often fast heartbeat).

"Apparently I was hallucinating, and the local doctor told me I was talking rubbish. I felt just so ill that I couldn't think of anything much except 'get me better'

Doctors were forced to put her in a coma so they could stabilised her blood pressure and assess the damage to her organs. Anne described herself as "basically conked out" for two weeks.

She gradually came round over a few days, and her health slowly returned. After nine weeks of near hell in hospital, Anne credits her quick treatment and the work of the NHS for surviving the deadly illness.

"If it is caught late it can do all sorts of horrible things. I am actually very lucky. I did feel depressed about it all when I was in hospital, wondering if I was ever going to get out, and was I ever going to get better."

"I'm very, very grateful to be alive."

Dr Fiona Agnew was less lucky, after contracting sepsis while pregnant along with her husband.

While he recovered, both Fiona and her child died from the condition, and her partner Craig Stobo started sepsis charity FEAT in her memory. It campaigns for awareness of the killer disease.

Fiona's death was sudden, as she died just two days after falling ill. She had not responded to the available antibiotic treatment, and Craig wants more research into tackling the tragic disease.

"To lose half your family overnight is something nobody should go through", he said.

"It's a very difficult thing to deal with, and I wanted something positive to come out of it and I'm very fortunate people have rallied round and there's a lot of support from friends and family."

Craig found himself asking what sepsis was, and was horrified when he was told that it kills around 18 million each year. He quickly decided to set a charity up in Scotland, with the aim of raising awareness and understanding of the condition.

"It is bewildering that more people are not more aware of it because everybody is aware of all the other major killers. It's almost been a silent killer for too long."

"What we're trying to shine a lot of sunlight on it to raise money and awareness so we can understand it better."