A stroke occurs when the blood supply to the brain is disturbed, resulting in damage to precious cells.
Around 150,000 people in the UK have a stroke every year, and more than 67,000 die from one.
Thousands more are left disabled and at least 300,000 people are thought to be currently living with moderate to severe disabilities following a stroke.
Several risk factors increase the chance of having a stroke, including being over the age of 65.
Diabetes and heart disease can also lead to strokes and people who smoke, are obese, drink heavily or have a poor diet or high cholesterol are also at higher risk.
Conditions affecting blood circulation, including high blood pressure, are linked to strokes, which can also be caused by the effects of an irregular heartbeat.
There are two main types of stroke - ischaemic and haemorrhagic.
Ischaemic strokes are the most common and account for 70% of all cases. They occur when a blood clot gets stuck in a vessel and interrupts blood supply to the brain.
Blood clots typically form in areas where the arteries have become narrow or have been blocked by the build-up of fatty deposits.
In contrast, a haemorrhagic stroke is caused when a weakened blood vessel supplying the brain bursts and causes brain damage.
The main cause of this type of stroke is high blood pressure, which can weaken the arteries in the brain.
A traumatic head injury can also lead to a haemorrhagic stroke, and stress can be a contributory factor.
Around 5% of strokes are caused by a condition known as a subarachnoid haemorrhage, which is caused by brain defects present from birth.
The signs of a stroke vary from person to person, but usually come on quickly.
Members of the public are encouraged to remember the word FAST, which stands for face, arms, speech, time, and can help identify somebody having a stroke.
The face may appear fallen on one side or there may be facial weakness, such as a dropped mouth or drooped eye.
The person having a stroke may not be able to raise both arms above their head and keep them there, and may be suffering from slurred speech.
Time stands for "time to dial 999" if the person is displaying any of these signs.
Other symptoms can include difficulty understanding what is being said, dizziness, problems with balance and co-ordination, difficulty swallowing and numbness or weakness in the body. The person may also fall unconscious.
Around 1.9 million brain cells are lost for every minute a stroke goes untreated, so getting prompt help is important.
One of the key treatments for ischaemic strokes - thrombolysis to dissolve blood clots - must be given within three hours of the start of a stroke to be effective.
Even people experiencing minor symptoms may go on to have a full stroke and must seek help.
Those people who have suffered an ischaemic stroke are usually given aspirin to thin the blood and cut the chance of further clots.
An anticoagulant, which helps prevent blood clots too, may also be prescribed.
Other drugs, including those that lower blood pressure and cholesterol, may be given, depending on the patient.
Some ischaemic strokes are caused by a blockage in the neck's carotid artery and may require surgery.
Patients who have suffered a haemorrhagic stroke are frequently rushed into theatre to remove any build-up of blood in the brain or to repair burst blood vessels.
The patient may then be put on a ventilator to help control swelling in the brain and give the body a rest while it tries to repair itself.
The process of rehabilitation following any type of stroke can be lengthy, and depends on the severity of the stroke and any resulting disability.
The damage caused by a stroke can be long-lasting and can affect both the physical body and the way the brain processes information.
It is possible for people to recover their former independence but it can be a long road to recovery.
A team of specialists are available to help stroke victims, including physiotherapists, psychologists, occupational therapists, speech therapists and specialist nurses and doctors.