Noticing hours that cannot be accounted for is read as a gap in memory or attention. Tradition links it to stress, autopilot living, or something you are not ready to look at.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.