A relapse is defined as "the appearance of a new symptom/s, of the return of old symptoms, for a period of 24 hours or more, in the absence of a change in core body temperature of infection".
The symptoms of a relapse vary and usually come on rapidly over hours or days and may last for several weeks. You will then have either complete or partial recovery.
The underlying cause of a relapse is inflammation of the myelin covering of the nerve fibres in the central nervous system (brain, eyes and spinal cord). Myelin is the specific covering on these nerve fibres and ensures that messages move quickly and efficiently from / to the brain or spinal cord. The symptoms experienced in a relapse will relate to the area of myelin on the nerve fibre that is affected.
Every person with MS is individual and it may be difficult to recognise the difference between a relapse and an exacerbation of symptoms (when old symptoms become worse but there is no inflammation or new lesions in the central nervous system).
It is helpful for you to note when and how the symptoms started, and any changes in your day to day lifestyle that might have affected your specific situation.
Steroids are sometimes used to speed up recovery from a relapse as they can reduce the inflammation and improve the chances of less long term damage.
It is important to report the symptoms to a health professional, your GP, neurologist or MS nurse.