No this is quite normal. I have this alot. Many times I'll see one thing that makes me recall an entire dream, usually one of the first dreams of the night considering I remember all the later REM cycle dreams well. I think that this sudden recall happens because we don't stress over recalling the dream. Hmm, isn't it odd how that works? We don't really care and realize that remembering a certain dream is no big deal, and bam, the entire dream comes to us without ANY effort at all. Something tells me that how the entire hobby of Lucid dreaming is in all.

I don't know, that's just my thoughts based off of my experiences with this occurrence.