How would you describe dizziness? Is it when you feel faint, or do you restrict it to times when you feel the world is spinning round? Or would you say it’s a ‘swimmy’ feeling, as if everything is moving randomly about you? Or would you describe all of these sensations as dizziness?

The answer you give is very important, because it matters a lot in deciding what is wrong and where the problem is. Take the feeling you get when you get up suddenly from a hot bath – you feel ‘light-headed’ and think you may faint.

Some people call that dizziness, but there is no sense of spinning. It’s quite different from the dizziness people describe when they have an inner ear infection called labyrinthitis. Then there is a definite feeling of spinning, and of loss of balance, but not of faintness; you don’t feel as if you are ‘greying out’.

We would call the first case faintness or light-headedness, and suspect something wrong with the blood flow to the brain. The second case we would label vertigo, and look for causes in the inner ear, or perhaps (much more rarely) in the substance of the brain itself.

Take two cases of my own as examples: The first happened many years ago. James, aged 55, was a roofer. On top of a three-storey building he suddenly had his first attack of vertigo. The world was spinning round fast from right to left, and he had to cling on to the roof to avoid himself, as he said later, ‘falling upwards into the sky’.

One of his workmates realised he was in difficulty and called me and the ambulance. He had to be levered away from his grip on the slates, and carried down to the street, where we were able to give him an injection to stop the vertigo.

He had bouts of dizziness after that for about six weeks, before they eventually stopped. That’s common for labyrinthitis, which is thought to be a virus infection of the inner ear, the organ,that helps us know where we are in space.

When it goes wrong the brain can’t co-ordinate what it receives from the eyes with what it receives from its ‘spirit levels’ of the inner ear and becomes confused.

We can treat that sort of dizziness fairly well with drugs similar to those we take for travel sickness, which damp down the messages we receive from our inner ear. It’s not so easy to treat the other type, where the circulation to the brain causes us to feel faint.

Which leads me to the second case: He walked into the surgery on a Monday morning, saying that he had been feeling unwell since the previous Friday evening. He ‘felt awful all the time’ but couldn’t pinpoint any specific problem, except that he was constantly ‘dizzy’.

I asked him if he meant that the world was spinning round him, but it wasn’t. He felt as if he was going to faint, although he hadn’t yet done so. If anything at all, there was a slight ‘swimmy’ effect when he stood up.

He had, until then, been healthy, and wasn’t on any drug treatments, so that I could rule out a reaction to a medicine. Naturally, the first thing we do when we hear a story like this is to take the pulse and blood pressure. It seemed he had a blood flow problem.

To my astonishment, his pulse rate was only around 30 per minute. Our hearts can’t operate at such a slow speed indefinitely. An ECG showed that there were several problems with the electrical conduction system in the heart – the series of cells that control the way the four chambers beat in unison.

Luckily, the story has a happy ending. He was taken to hospital and was fitted with a pacemaker that controlled his heart rate and he felt much better immediately.

So if you are feeling generally unwell, but can’t pinpoint why, don’t hesitate to see your doctor. I’d make two more points: My second patient felt unwell over the weekend,waited until Monday to see his own doctor, rather than call in the 24-hour service. That wasn’t a good decision, although it is understandable. Don’t hesitate to call the emergency services if you really feel ill, even if you can’t understand why you do.

The second is that it is wise to be able to take your own pulse. If you know where to take it at the wrist, and how to recognise when it is beating too fast, too slow, or erratically, it could help you make the decision to seek help.