A deep trance in which an injured Vulcan focuses all bodily resources on healing, appearing close to death, and from which the patient must be roused by being struck hard.
The healing trance is a Vulcan technique of self-hypnosis used after serious injury. The patient withdraws from the outside world and concentrates blood, strength and antibodies on the damaged organs. To an observer the Vulcan seems to be sinking into a fatal coma, though some awareness of the surroundings remains.
It is shown in the original series episode A Private Little War. Spock is shot with a flintlock on Neural and returned to the Enterprise, where Doctor M'Benga, who trained in a Vulcan ward, takes charge of the case and warns Nurse Chapel what to expect.
When Spock begins to surface he asks her to hit him, since pain is what brings a Vulcan fully back to consciousness. Chapel slaps him hesitantly; Scott walks in and pulls her away in outrage, and M'Benga has to finish the job himself with a series of hard blows before Spock sits up, cured.