Breathing difficulty, known as dyspnoea, could be caused by a problem with the heart or airways.
It could be caused by an asthma attack, where the airways narrow. More phlegm is made than usual, and sufferers could wheeze and cough.
Pneumonia may also develop after a problem in the airways. The condition includes swelling of the lungs, and is usually treated with antibiotics.
If you suffer form chronic obstructive pulmonary disease – which includes conditions like emphysema and bronchitis – the dyspnoea could be a sign that the condition has worsened.
Shortness of breath may be the only warning sign of a heart attack, according to the NHS.
You should see your doctor immediately if you think this may be the case.
Breathing difficulties could also be caused by heart failure. This is where the heart becomes too weak to pump blood efficiently around the body.
Heart failure leads to water building up in the lungs, making breathing difficult.
More uncommon causes of shortness of breath include anaphylaxis, and a partially collapsed lung.
A pulmonary embolism may also be the cause of the problem – where one of the blood vessels in the lung becomes blocked.
The symptom may also be a sign of a panic attack, or deep anxiety.
Patients are advised to try and breath slowly during a panic attack, or to breath into a plastic bag.
If you suffer form shortness of breath, you should call your doctor immediately.
Your GP can assess you over the phone, and could admit you to hospital.
The NHS advises patients to not ignore long-term shortness of breath, as it’s likely to be a symptom of a deep-lying problem.
That includes obesity or asthma.