Once you have witnessed someone having a stroke, you will never be unsure again as to what has happened to cause a person's sudden collapse.

One day last year, after a bowls match, I was sitting next to Jim, a visiting player, enjoying a cup of tea and chatting with him and the other people round the table. I had just shared a joke with him - he was a very lively gentleman of about 75 years of age - and looked away for a moment when sombody asked me to pass the sugar. When I looked back, my neighbour just wasn't there any more.

Of course, Jim was still sitting there in his chair, but the person I had been chatting and joking with a second before seemed to have left the room. In that short time, he had suffered a stroke.

He was able to talk, but his voice was much quieter and slightly slurred. He complained of having a headache, and would I fetch his paracetemol tablets from his jacket in the changing room? When I got back, he had slumped down in his chair and was dribbling from the corner of his mouth. Somebody then phoned for an ambulance and it was not long before the patient was getting proper medical attention, beginning with a good whiff of oxygen.

A stoke involves a loss of blood supply, and therefore oxygen, to a part of the brain. This is usually caused either by a blot clot in an artery or a rupture of a blood vessel in the brain. The usual result is a loss of feeling on one side of the body, which accounts for the dribbling from the mouth as muscle control is lost. Depending on the severity of the stroke, the symptoms range from "pins and needles" to complete paralysis.

Jim had taken his paracetemol pills to the bowls match because he had had a slight headache for much of the day. However, he felt well enough to drive to the match, and had just played the match without any problems. He would have done better to take an aspirin-based treatment, because aspirin has a very quick effect on improving blood flow. At the time of the stroke, he was most aware of his headache having suddenly become much worse.

Experiencing a stroke is a frightening experience. You have suddenly lost control, your body won't do what you what you are telling it to do, you may feel dizzy and disoriented, and your vision may be blurred. This means that, as a witness to a stroke, you need to be aware that your questions may not get a sensible answer. It is not that the victim does not want to answer your questions, he may not understand you, and may not be able to respond.

You must therefore do what you can to reassure the patient while waiting for the paramedics to arrive. Keep talking to them, even if you get no response. Don't try to move them - if they are sitting down, keep them sitting and don't try to make them lie down.

Fortunately, Jim's stroke was not too bad. He spent a night in hospital, under observation, and was sent home the following day. He would have been put on a course of drugs to help prevent future blood clots and given advice on any necessary lifestyle changes.

Some people suffer a series of "mini-strokes" over a long period of time. These may be so small that the patient may not even know that they have happened, but, each time, a little more brain function is lost. The end result may be similar to dementia.

One of our own bowls club members has been a victim of mini-strokes, and another has had to change from being left-handed to right-handed, due to loss of coordination on one side of his body.

It is important to be able to recognise the early symptoms of stroke, because rapid treatment can make a huge difference to the recovery of the patient. I am not medically qualified, so I can only offer "first aid" advice. For more information about stroke, I suggest that you view the excellent layman's guide offered by the BBC. This covers measures you can take to decrease your chances of getting a stroke, as well as the treatment that is available to sufferers and the help that carers of stroke victims can call upon.