When related to haemorrhage, the lucid interval occurs after the patient is knocked out by the initial concussive force of the trauma and then temporarily recovers, before lapsing into unconsciousness again when bleeding causes the haematoma to expand past the extent for which the body can compensate. After the injury, the patient is momentarily dazed or
knocked out, and then becomes relatively lucid for a period of time which can last minutes or hours. Because a patient may have a lucid interval, any significant
head trauma is regarded as a medical emergency and receives
emergency medical treatment even if the patient is conscious. Delayed
cerebral edema, a very serious and potentially fatal condition in which the brain swells dramatically, may follow a lucid interval that occurs after a minor head trauma. Lucid intervals may also occur in conditions other than traumatic brain injury, such as
heat stroke and the
postictal phase after a
seizure in epileptic patients. ==See also==