Do you become unconscious for a spit second when you sneeze?

Normally, no -- you don't. Extremely strong sneezes, or personal physiology can -- very rarely -- cause vasovagal syncope (this appears to occur when the pressure on the carotid sinus -- the network that monitors blood pressure in the carotid artery -- detects an "overpressure", and sharply reduces blood pressure), which may result in unconsciousness. But again -- this is the exception.