Trousers are read as practicality and who “wears the trousers” — authority and decision. Losing them in a dream is traditionally read as embarrassment or fear of losing control.
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.