I had a very similar dream the other night. Near the end of the dream I was in my room, became lucid and changed the time on my clock. As soon as I realized what was going on I also started to become aware of my sleeping body and the vividness was gone and then I woke up (maybe dreaming of being in my room made it harder to stay lucid).

I think what happened was that in the dream I was mainly focusing on what I was seeing and completely ignored my body - this would explain the "3rd person" feeling. If this happens again the first thing I'll do will be to look at my hands, then focus on my breath. That way I can try to integrate all my senses and keep my mind calm, and I'll remind myself the whole time that it's a dream.
It takes practice - I hope this helps