Anaesthesia or anaesthesia (from Greek “without sensation”) is a state of controlled, temporary loss of sensation or awareness that is induced for medical purposes. It may include some or all of analgesia (relief from or prevention of pain), paralysis (muscle relaxation), amnesia (loss of memory), and unconsciousness. A patient under the effects of anaesthetic drugs is referred to as being anesthetized. Anaesthesia enables the painless performance of medical procedures that would otherwise cause severe or intolerable pain to an unanaesthetised patient, or would otherwise be technically unfeasible. Three broad categories of anaesthesia exist.