Stuart Murdoch remembers feeling as though he had simply "disappeared".

It was the late 1980s and the Glasgow University student - who would later go on to front one of Scotland's most successful indie bands, Belle & Sebastian - found his previously full life being swallowed up by myalgic encephalomyelitis, better known as ME or Chronic Fatigue Syndrome.

"It was quite gradual, almost over the course of a summer," said Murdoch, who was 21 when the symptoms set in.

"I did athletics so that was a really good barometer. I suddenly realised I was knackered and I'd never been knackered before.

"I'd had so much energy but I felt my legs giving, and by the end of the summer I'd given up the running.

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"Everything sort of caved in one after the other. First it was the athletics, then it was going our recreationally, then it was my job, and finally I struggled through the university course, did the exam and then that was it - I was out of the game.

"It was a very isolating experience. I shed all my friends and all the people I knew simply because I ended up back at my folks' house, back in the bed I'd slept in as a kid.

"I just disappeared."

The musician, writer and filmmaker, originally from Clarkston in East Renfrewshire, will perform with Belle & Sebastian at the first-ever 'Millions Missing' event in Glasgow on May 12. The rally aims to raise awareness of the desperate need for biomedical research into ME.

The condition affects some 21,000 people in Scotland but there are currently no known effective treatments, diagnostic tests or even any clear evidence on exactly what triggers it.

In Scotland, ME is the main cause of long-term sickness absence from school but there are no ME specialist hospital consultants and only one specialist nurse.

Professor Chris Ponting, who will also take part in the Millions Missing event in George Square, is one of those trying to unravel the ME enigma.

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Prof Ponting, an expert in disease genomics at Edinburgh University, is currently leading a study to comparing the immune systems of individuals with ME against healthy participants in the hunt for an ME "signature".

He said: "We don't actually know where the seed of this disease is. Is it in nerve cells, is it in immune cells, is it to do with the 'battery' of the cell called the mitochondria?

"There are a lot of indications as to what has gone wrong, but actually what the cause or the set of causes are, we don't know.

"In the immune system study, we are basically saying 'is there evidence that the immune system has been challenged in people with ME?'. Because whenever the immune system is challenged with a virus for example it reacts, it learns, and it's changed.

"And we can tell that that has happened - even in the past - by looking at the immune cells and seeing how they differ from people who are healthy or have a different disease."

Prof Ponting is also involved in efforts to set up a UK-wide genetics study into ME, which he hopes to see launch in 2020.

He added: "We have to find ways to treat people because there are a quarter of a million people in this country who have this disease. The loss to our society, even the financial cost, is over £3 billion a year. One in 200 people have it. It's such a major problem we have to find some answers."

Now 50, Stuart Murdoch said it was becoming a father for the first time in 2013 that led him to want to share his own experience after years spent trying to ignore his illness.

"I had better years in between, with the band," said Murdoch. "I think I had a baseline level of energy and I was just very careful.

"But then I got married and when we had a kid the ME sort of 'found me out'. I really struggled.

"I knew it was a risk, but we had a kid and we've got two now. It was a risk worth taking, but it really set me back.

"It's hard for me to keep up and we did have to get help, but it really made me want to engage again.

"For years when I was feeling better in the 2000s, I didn't want to think about it. I had a lot of people writing to me and I was reticent because I thought 'no, I feel okay, I'm coping' - I didn't want to go back there. I wanted to tell myself I didn't have ME anymore.

"But now that I've been 'found out', I really want to talk about it. I think it helps other people."

Gillian Grant, an MEAction volunteer and organiser of Millions Missing, said she was thrilled to bring the event to Glasgow.

She said: "Our key aim for Millions Missing is to raise awareness of the desperate need for funding for biomedical research into ME. It is vital that we have appropriate ring-fenced funding for biomedical research into the underlying cause of the disease, the discovery of biomarkers for diagnosis and ultimately the development of effective treatments.

"I hope that the contribution I make will help to not only change my circumstances but in time, will change the care and treatment offered to people living with ME in Scotland and this gives me some hope for the future."