Being unable to speak at all is read as silenced feelings or a truth you have been kept from telling. Dream books also link it to awe — being left speechless.
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.