Briefly, as measured in milliseconds I will buy in the case of clean decapitations. When there is a total loss of blood pressure as in the case of decapitation then the victim would lose conscienceness almost immediately, even if not cliniclly dead.
Even during fainting blood pressure is not lost so rapidly and anyone can see the results of that.
When speaking of a decapitation due to an explosion as is referred to in this article then conscienceness would be lost instantaneously due to concussion.
The chemicals that carry our thought processes do not work well at all when violently forced several centimeters off course. The bombers brain was effectively turned into the consistency of runny jello the minute the explosive wave hit his head.
If this is true it's jolly for you,
your courage screw to bid us ado.
I'd bet it was runny jello BEFORE the explosion.