Robbie Donnelly, from Portland, ran the Great South Run after his AVM was misdiagnosed as a migraine

Robbie Donnelly, of Greenways, visited Weymouth walk-in clinic last Saturday, the night before the run, after experiencing a severe headache and loss of sight whilst driving.

After being told it was a migraine, Robbie drove to Portsmouth the next day to run the ten mile race, consequently putting his life in extreme danger.

The 33-year-old said: "On the morning of the run, I just had a mild headache so I thought the nurse practitioner must have been right and I went ahead with the race.

"At about the six mile mark I started to feel really bad, but I finished the race. I actually beat my time and ran the race in 1hr 27mins which I was really pleased with."

Still feeling unwell the next morning, Robbie visited his GP who suggested he have a CT scan at Dorset County Hospital.

It was there Robbie discovered he actually suffers from brain arteriovenous malformation (AVM), an abnormal tangle of blood vessels that diverts blood from the heart away from the brain to the veins.

An extremely rare condition, AVM is only found in one per cent of the population with 12 per cent of those affected experiencing symptoms with varying severity such as headaches, seizures, dizziness and muscle weakness.

More seriously, as in Robbie's case, they can burst causing bleeding to the brain, leading to an intracranial haemorrhage and potentially brain damage or a stroke.

Robbie said: "The problem with AVM is that the symptoms are just like a headache and a lot of the time it is misdiagnosed which is what happened to me. If my GP hadn't sent me to DCC I could be in a very different position right now."

Following the scan, Robbie was transferred to the neurological unit at Southampton General Hospital for a more thorough examination.

He has now been signed off work and diagnosed rest until an operation to remove the AVM in mid-December.

Robbie has spoken out about his experiences in the hope he can raise awareness of the rare condition.

He said: "While the risk of what happened to me is very slim, I want to raise awareness because of the misdiagnoses.

"I want people to be aware that if they suddenly experience a severe headache, especially if they have never suffered headaches before, it is always worth asking your doctor for a CT scan.

"Doctors call the headache a 'thunderclap', it just comes out of nowhere and feels like you have been hit around the head with a steel pole."

Dorset Healthcare University Foundation Trust which operates the Weymouth urgent care centre has been contacted for comment.