A lucid dream could be no more complex than this. You are at work and do not understand how to operate some equipment. You get frustrated because you normally can. It is very odd, so odd infact that,,, "maybe this is a dream?" You look around. The work crew is wrong; your brother is there. It makes no sense. You suddenly realize "Holy F$%K! This is a dream!" The shock of it wakes you up.

The fact that in that dream you eventually knew it was a dream and not real life is what makes it a Lucid Dream.