Anaesthesia means 'loss of sensation'. Drugs that cause anaesthesia are called anaesthetics.
Anaesthetics are used during painful examinations and surgical procedures. They prevent the nerve signals, that keep us awake and aware or that transmit pain, from reaching our brain. They switch off sensation in certain areas of the body and induce sleep.
A lot of medical procedures are performed under anaesthesia. Local anaesthesia and general anaesthesia are two common types of anaesthesia. General anaesthesia involves inducing artificial sleep. In this state of induced sleep, procedures can be performed without you feeling anything.
Once the anaesthesia wears off, nerve signals can reach your brain again and consciousness and sensation return.