Dreams like yours can be rich in symbolism and often reflect your subconscious thoughts, fears, and experiences. Here are some possible interpretations of the elements in your dream:

1. Threatening Environment: The gang in hoodies may symbolize feelings of vulnerability or anxiety about external threats in your life. This could relate to social pressures, fears about your safety, or concerns about fitting in.
2. Escape and Guidance: The act of trying to escape to your grandparents' house suggests a need for comfort and safety. Grandparents often represent wisdom and protection, indicating you might be seeking guidance or stability in your waking life.
3. Impossibility of the Journey: The notion of driving from California to Europe highlights feelings of being overwhelmed by challenges that seem insurmountable. It could signify aspirations or goals that feel out of reach.
4. Meeting Authority Figures: Encountering someone claiming to be the secretary of defense could reflect your thoughts about authority, politics, or protection. This character may represent a desire for assurance or security in a chaotic environment.
5. Breaking Social Norms: Breaking into a house and pretending to be normal at a birthday party suggests a conflict between your real self and societal expectations. It may indicate feelings of rebellion or a desire to escape from routine life.
6. The Horse Tradition: The chaotic image of a horse running rampant could symbolize uncontrolled emotions or situations in your life. It might point to a sense of unpredictability in your environment or relationships.

Overall, this dream could reflect your feelings of anxiety, the desire for security, and perhaps a struggle between societal expectations and personal freedom. Consider journaling your thoughts and feelings about these themes for further insight.