Automatism can be caused by physical compulsion (being thrown or pushed), or illness, or uncontrollable reflex action, or blackout.

In Hill v Baxter [1958] QBD, D, for some reason, perhaps falling asleep whilst driving his van crossed a stop sign and hit another vehicle.  He would not have been guilty if he had lost control when attacked by a swarm of bees; Devlin J

...like an uninvited swarm of bees...

Lord Goddard in Hill v Baxter [1958]

"I do not mean to say that a person should be made liable at criminal law who, through no fault of his own, becomes unconscious while driving, as, for example, a person who has been struck by a stone or overcome by a sudden illness , or when the car has been put temporarily out of his control owing to his being attacked by a swarm of bees..." I agree that there may be cases where the circumstances are such that the accused could not really be said to be driving at all. Suppose he had a stroke or an epileptic fit, both instances of what may properly be called Acts of God; he might well be in the driver's seat even with his hands on the wheel but in such a state of unconsciousness that he could not be said to be driving. A blow from a stone or a swarm of bees I think introduces some conception akin to "novus actus interveniens".

So Automatism is something external that the defendant does not bring upon himself.

Not one bee, but a swarm, because it has to be total loss of control

If the defendant loses control because of an illness, that is, some internal factor, he can only plead insanity.

Acts or omissions must be voluntary, if they are not it is called 'Automatism'

D must be in control of his movements – not thrown, or slip, or be dazed – for his actions to constitute actus reus; even in a case of strict liability.

Automatism is  '… not merely a denial of fault. It is more a denial of authorship . . . in these circumstances, it is fair to say that this was not D's act, but something which happened to D'

Voluntary conduct not always required in Strict Liability offences.

There are many offences of strict liability, in which no fault element need be proved.

In such cases, one can therefore have an actus reus without any corresponding mens rea.

In Larsonneur (1933) L, a French woman was prevented from entering into a marriage of convenience. She went to Ireland, but was brought back to England by Irish police she was guilty of 'being found in the United Kingdom' in breach of an order excluding her.

The circumstances under which she was returned were 'perfectly immaterial'.

Winzar v Chief Constable of Kent (1983). D was 'found drunk on a highway', having been removed from a hospital by the police officers who then arrested him in their police car 

Automatism does not include self induced intoxication, even though the accused may not be in control of his muscles.