Accompanying fever and/or vomiting or neurological features such as confusion, slurred speech, change in personality, weakness, visual disturbance or seizure ?

These include any unexplained visual disturbance, including double vision, a seizure, numbness or weakness, loss of balance, stumbling, changes in speech, odd behaviour and impaired hearing or sense of smell.

Warning signs are headaches, blurred vision or visual disturbance, abdominal or shoulder pain, nausea, confusion and feeling short of breath.

Even now, five minutes' cycling on a static bike with no resistance or running the length of the pitch brings on the symptoms: headache, visual disturbance and vomiting.

The seizure aura might also occur as a visual disturbance, such as tunnel vision or a change in the size of objects (macropsia or micropsia).