Automatism is a person acting in an automatic, "mechanical" way. Their acts must be involuntary.
Involuntary: "An involuntary act means an act which is done by the muscles without any control by the mind, such as a spasm, a reflex action, or a convulsion".
Automatism can also come from an external factor. Hill v Baxter.
Automatism cannot be self induced by things like drugs.