This word comes from the base words ‘para’, which means “altered” or “abnormal”, and ‘aisthesis’, meaning “perception”. Most people are familiar with this sensation – it commonly occurs when a person has slept on their arm or left their legs crossed for too long. The feeling is caused by sustained pressure on a nerve. Paresthesia is typically fleeting, but if it lasts a long time or occurs frequently a medical condition is likely to blame. Chronic paresthesia can be caused by a neurological disease or traumatic nerve damage.