The carotid artery gets its name from the Greek karos, which means "deep sleep or stupor". The term was already being taught in Roman medical schools early in the first century A.D., and was quite possibly used by the Greeks 300 hundred years earlier as it was Aristotle (384-322 BCE) who first noted that pressure on the both carotid arteries could induce a stupor.
Galen claimed, from the results of his experiments, that carotid pressure did not produce any kind of stupor. However, he probably was basing his observations on the response of ruminants which have a very effective collateral blood supply to the brain through a number of vertebral vessels; consequently they don't show a loss of consciousness even with prolonged pressure applied to the carotids.
In humans, the "blood choke" (carotid restraint) in which both carotids are compressed typically leads to unconsciousness in around 10 seconds. Once pressure is removed, consciousness is regained in 10-20 seconds