Honestly you could just lack the awareness to notice. That's not a slight against you, acute awareness in the dream state is not an innate ability and must be practiced frequently in order to be successful with it.

In any dream state, you can test the rules of the world around you and see that your brain doesn't quite build the world to completeness. Light switches will not work, text will morph and shift either in front of your eyes or when you look away and turn back, the people around you will spontaneously morph into others, you can breathe through your nose when it's plugged, etc.

What happened to you is referred to as a false awakening. Testing the reality of your situation by checking clocks, breathing through your nose, counting your fingers, etc. will all quickly put you into a more lucid and aware state. From there you either continue or, more commonly, you wake up.