FLASHBACKS, nightmares, panic attacks and exhaustion are all symptoms that can plague sufferers of post-traumatic stress disorder (PTSD).

It is a term that has only emerged in recent years and one that the World Health Organisation has defined as a "delayed or protracted response to a stressful event or situation". It can manifest in a person in numerous ways.

For former member of the Royal Navy and UN Military Observer and now professional artist, John McDermott, 54, reliving past trauma, difficulty sleeping and panic attacks are the ways PTSD continues to take its toll on him four decades after he signed up.

Witnessing the horror of the killing fields in Cambodia, the aftermath of the genocide committed by the Khmer Rouge and "seeing a rubbish tip of human bones" was the catalyst that sparked a mentally tumultuous response to decades of stressful experiences of war – many he still cannot talk of today.

When PTSD began to take over he found himself on an extended journey in search of treatment. What he said the military gave him was two days relaxation in hospital on the floor with a pillow listening to soothing music. "It didn't do anything to help," he said.

Frustrated by the lack of urgency, attention and help that sufferers are given, John founded not-for-profit social enterprise Aftermath PTSD, and is committed to raising awareness of the condition through art exhibitions.

"I joined the Navy when I was 15 and was on board my first ship when I was 16," he said. "When I was 17 I was involved in a Turkish invasion in Cyprus.

"A Turkish warship had been sunk by its own aircraft and it was our job to search for the bodies and fish them out of the sea. That was my first experience."

A year later, in 1975 he was deployed on HMS Achilles to Vietnam to facilitate the evacuation of Europeans and South Vietnamese from Saigon who were under vicious attack from the Viet Cong.

"The North Vietnamese were coming down at rapid rate," he said. "We were stationed off the coast with other boats acting as platforms for helicopters to land.

"But what followed was a scene of total chaos. The platforms were so full helicopters couldn't land and were just ditching in the sea.

"It was awful. We were listening to them on the radio and you could hear their panic."

John said when he returned home it was impossible to talk to the family and friends he had left behind about what had happened.

Aged 25, John was the leading gunner aboard HMS Plymouth, one of the first ships to be detached to the Falkland Islands to protect the landings from air attacks.

"I remember the signal very clearly, 'prepare for war, your life will depend on it'. It was that simple," he said.

"We loaded as much ammunition on the ship as possible.

"Every day we were being attacked and watched other ships being hit.

"No one was sleeping.

"Every day we'd see a ship get hit and we thought our number would be up at any time.

"We were eventually hit on June 8, by four 1,000lb bombs and a number of 30mm cannon hits.

"So protection turned into fighting for survival.

"I was exhausted when I came home. We'd run out of rations and were having one meal a day so we were all physically weak.

"Lots of guys started to suffer from severe stress but I thought I was fine.

"By 1992, I had become really sick. I realised that I'd probably been responsible for a lot of people's deaths but I didn't share this with anyone.

"So I volunteered to become a UN military observer.

"I was sent to south Cambodia in the aftermath of the genocide to encourage disarmament and democratic electoral process."

John said there are some things he still cannot bring himself to talk to about.

"I just don't want to go there," he said.

He says discovering mass graves was among some of the most distressing and disturbing experiences of his career.

"It was like seeing a rubbish tip of human bones," he recalled. "And remains which pigs were rummaging through. It was disgusting and horrifying.

"I came close to dying three times out there."

It was when he came home that years of traumatic experiences took their grip on John's wellbeing.

"I was having about six major panic attacks a day. I thought I was going mad. I also thought I was going to die," he said. "It felt like a heart attack, pain in the chest, shallow breathing, and feeling like I was going to collapse.

"That's what made it so terrifying. I had sleeplessness, flashbacks and this was because of my experiences in Cambodia, but as I later found out, it had really been accumulated over years and maybe Cambodia was a catalyst for me, but I still stayed in service, because I kept it hidden, and masked it as best I possibly could.

"I didn't know what was wrong with me. I hadn't even heard of PTSD.

"I started to get very ill but could no longer hide it.

"What really stuck in my mind and made me sad was that people who had a high regard for me started looking at me cautiously and with suspicion. I felt very, very let down. When I needed help most, I didn't get it."

It was only when John paid to see a psychiatrist that he was told he was showing all the signs of PTSD.

"He told me to see a military doctor, which I did," John said. "And what I got was two days relaxation in hospital on the floor with a pillow listening to soothing music. It didn't do anything to help.

"I found some personal strategies to cope because I didn't want to lose my job. It was my livelihood and I had a young family growing up and I was dedicated to the Royal Navy.

"I didn't want to be viewed as just another basket case."

Despite what he was going through, John was posted to Bosnia and then to Sierra Leone on HMS Cornwall for eight months.

"A lot of eventful things happened there that didn't make me feel any better," he said.

"About a year later I came out of the Navy, I was still seeking help for my condition from all the sources I could think of. I was constantly going through therapies I was paying for myself.

"People with a broken leg could get help. But people with a broken mind couldn't. But what's the difference?"

John suffered a serious breakdown in 2008. It was then he turned to the charity Combat Stress, which diagnosed him with having PTSD.

"I didn't realise how badly. I got there just in time. I don't think I would have survived any longer," he said.

"Forces personnel are heavily dependent on charities rather than the Government providing a full duty of care.

"The reality is that there are five-and-a-half million veterans in this country so we need to draw a line under what a duty of care really means. It shouldn't be the job of the charities.

"The number of people suffering from combat-related trauma is high and it's turning out to be a national disgrace, and this has been voiced by the Royal British Legion who have called this the 'perfect storm'."

Some of John's work is being exhibited as part of War Art, an exhibition showcasing more than 100 paintings from both serving and ex-serving forces personnel.

The exhibition, at Exeter Castle, will be on show until Sunday.