For six years, Nancy Greig struggled alone with an unknown illness that saw her lose weight, suffer exhaustion and left her in agony.

On the surface she appeared to be in good health, with colleagues remarking how great she looked thanks to her seemingly effortless weight loss.

Her body hid a life of sleepless nights and severe pain, however, punctuated with frequent trips to the toilet running into double figures each day.

"I'd feel shattered, I'd feel awful inside and I'd know that if I looked at myself in the mirror I would see that I wasn't well but other people don't really see that," she explains.

When Nancy turned 30 she finally decided to visit her GP, who diagnosed her with ulcerative colitis, a condition her father began suffering from at roughly the same age.

Along with Crohn's disease, ulcerative colitis is one of the main forms of inflammatory bowel disease (IBD), which more than 26,000 people in Scotland suffer from.

A lifelong chronic illness, ulcerative colitis causes the surface of the inner lining of the rectum and the colon to become inflamed with tiny ulcers, which may bleed or produce pus.

Those who have the condition can suffer from pain, fatigue, loss of appetite, anaemia and diarrhoea.

For Nancy, the assumption following her diagnosis was that a prescription medication would ease the painful and upsetting symptoms of an illness that was invisible to others from the outside, but frequent flare-ups of her condition often saw her admitted to hospital.

She recalls one occasion as she walked through the ward to stretch her legs when a doctor commented on how well she looked.

"He said: 'Oh, oh it's you, I thought you were one of the junior doctors there for a minute, you look so well, how many bowel movements have you had today?'

"It was like he couldn't believe that I could be walking around looking normal but inside I was so sick."

While on the outside Nancy continued to look healthy, by the age of 34 she was forced to have an emergency colectomy and ileostomy. As a result, she now wears a colostomy bag to collect waste from her body.

Four years later, with a stoma bag hidden most of the time underneath her clothes, Nancy's ulcerative colitis is practically undetectable.

Yet she still finds it frustrating that she feels she cannot discuss her condition freely with people who find the subject uncomfortable.

"When I was ill, I would be in the company of someone and they would ask me how I was and I would say, 'I'm not very well I've been s*****g blood for the last three months.'

"Whereas if I had said, 'I'm not very well, my arthritis is playing up and I have to use a stick', then they'd say 'that's awful' but they just want to change the subject if you told them the reality of what was going on."

The frustrations of dealing with a lifelong hidden illness like ulcerative colitis are also met with embarrassment when it comes to using public bathrooms.

A disease which sees sufferers urgently require access to a toilet, using a disabled or accessible facility is often preferred for privacy but can be met with looks or comments when their ailment is not outwardly visible.

Nancy says: "As far as I'm concerned, I've got a right to use a disabled toilet or an accessible toilet if I want to if I feel that is going to be more convenient for me.

"[I would use an accessible toilet if] for example I needed to actually change my bag because I had a leak or I felt that I was going to be particularly self-conscious about the smell, so I would maybe prefer to go into a toilet that was completely enclosed.

"If somebody did challenge me I would be quite happy to actually show them my stoma bag because I think people need to be educated.

"Not everyone who uses a disabled or accessible toilet is visibly ill or has a walking stick or a wheelchair or some kind of mobility issue, there are a lot of reasons why somebody would need to use a toilet like that."

David Barker chief executive of Crohn's and Colitis UK says the embarrassment and stigmatisation people with hidden illnesses face is something that needs to be addressed, encouraging discussion of inflammatory bowel diseases to help reduce the stigma sufferers face.

"I would say think twice [before making a judgment]," David adds. "People who use these facilities are not always in a wheelchair, there are a number of hidden conditions, Crohn's and colitis is one where people have that urgency to use the bathroom. It is a disability."

As part of World IBD Day on May 19, Crohn's and Colitis UK are calling for more support for sufferers of hidden illnesses.

There are just 45 specialist IBD nurses across Scotland, each with a potential patient load of 500 people.

David explains: "The difference they make is huge, yet there are nowhere near enough of them so we're working with gastroenterology teams, with the government, with patients and our job is to ensure that ultimately every patient has access to an IBD specialist nurse."

Nancy believes that the support of a specialist nurse would have helped her cope with her diagnosis better, adding: "I think it was a combination of a lack of understanding and lack of services that I found most challenging for me."

After four years of living with a stoma, Nancy says her quality of life has improved dramatically. While she will need to return to hospital at some point for further surgery, she doesn't experience any of the symptoms she did when she was first diagnosed.

She said: "It can be quite hard to adjust to something like that and in the grand scheme of things I think it has been a vast improvement to the quality of my life.

"Now I can do what I want, when I want. I can use public transport, I can go out, I can eat out, I can go to work normally.

"Having a stoma doesn't stop me from doing anything."