Forty-two-year-old Willem went for a routine training run - and suffered a sudden cardiac arrest.
The dad-of-one was clinically dead for 15 minutes - and only learned of his fate when he woke up 10 days later in a hospital intensive care unit.
He had no previous health problems. “I’m very very lucky to be alive,” he said. Very few people survive out-of-hospital cardiac arrests.
Now - one year on - Willem is slowly trying to piece back together his life and is campaigning for more people to learn life-saving CPR, cardiopulmonary resuscitation, skills - and for more defibrillators to be sited in public places.
When his attack struck, Willem, who works in IT for a financial services company, had left his home in Bartholomew Way, Horsham, in training for the Brighton 10k run.
He was running past the Rising Sun pub in Pondtail Road when he collapsed. “I was found by some people in the pub and they rang 999,” said Willem. “Nobody knew CPR.”
It took an ambulance six minutes to reach him and another nine minutes to get his heart going again. “Nobody really knows why it happened.”
He had always considered himself fit and healthy - “I’ve never been a guy who took medication; I’ve never smoked and I’m a moderate drinker” - and enjoyed a range of sports including squash, tennis, cricket, golf and snowboarding.
After his cardiac arrest, he spent 10 days in intensive care in Brighton. Now he is gradually picking up the pieces of his life but is still suffering from the after-effects of his ordeal.
He has suffered personality changes because of a lack of oxygen to his brain when his heart stopped.
“I struggle massively with fatigue,” he said, “and I haven’t been able to work since it happened.”
He also suffers memory loss and has no recollection of his actual cardiac arrest. “My brain seems to work in black and white now. I see things as good or bad, right or wrong.
“I used to be a very empathetic person, but now I seem to have lost a lot of that. I have anger issues. It has changed me as a person quite a lot. I am very different to the way I used to be.”
Willem now hopes to meet up with the ambulance crews that saved his life. “I feel very indebted to the people that found me and also the paramedical services.”
Meanwhile, he is receving help and support from a Facebook group known as Sudden Cardiac Arrest UK. Members staged a Guinness World Record Attempt earlier this month to get the largest number of cardiac arrest survivors in one place.
l Free first aid advice is available from St John Ambulance online - including how to learn CPR - at www.sja.org.uk/firstaid
St John Ambulance also has a free first aid app which can be downloaded from your app store, which gives life saving advice at your fingertips.