A slap is read less as violence than as a sudden wake-up: a remark that stung, or a truth delivered too sharply. Giving one is traditionally seen as frustration that has not found calmer words.
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.