Being unable to distinguish between wake and sleep states is actually very dangerous. And reality checks CAN fail!! The brain is not perfect! If someone is awake and believes they may be dreaming a reality check is not always going to work as discearnable proof that the person is awake. The brain can play tricks on us and it is especially likely that someone who is having difficulties distinguishing between reality and dream states may be having hallucinations- visual, or auditory, mild or severe. Hallucinations are not reserved for schizophrenics and are quite common. Infact hallucinations at one time were necessary for human survival and we hallucinated before having conscious thought. (am I losing anyone?)

I have often thought about the dangers of lucid dreaming and this is the one that always disturbs me.