When we cut ourselves, the blood naturally forms a clot to stop the bleeding. Sometimes an unwanted clot can form in a vein deep within the leg. This is called a deep vein thrombosis (DVT).

Occasionally this can lead to serious (and sometimes fatal) complications such as pulmonary embolism (PE). This is where a clot breaks off and travels in the blood to the lungs.

Immobility is a major cause of deep vein thrombosis. It is occasionally associated with long-haul flights because this involves sitting for long periods of time in a restrictive position. When you are admitted to hospital, there is a higher risk of DVT/PE than usual.

• Our video guide to DVT and PE