I have had it happen as shallow as 10m (33ft). It really depends on your physical readiness before the dive. Lack of sleep, being hungover, hunger, dehydratio

I have had it happen as shallow as 10m (33ft). It really depends on your physical readiness before the dive. Lack of sleep, being hungover, hunger, dehydration can all contribute to narcosis. Fortunately it is pretty hard to miss once you have experienced it a few times. If you ever experience just go up a couple meters and the symptoms should dissipate.