I really dont think its a good idea holding your breath. Without breathing I could die (I wont say you, because I dont want anything to happen to you). It could be and this is only a 'could be' so not really true, or well it could be, but I doubt it, that when you hold your breath your brain goes into hyperdrive like 'what the hell is going on , where is my oxygen' and chemicals are released and parts of the brain are shut down to conserve what little oxygen is there , so it could be the part of your brain that looks after hallucinations and mental fatigue are switched off.

Now Im thinking it would have been a good idea if we were built with switches and we could switch stuff on or off. like our feelings. Maybe in the future.