Forgetting your lines is a classic anxiety dream. It is traditionally read as fear of being unprepared or exposed, and as worry about failing in front of others.
When this appeared in your dream, what were you feeling?
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.