Dreams involving car accidents, particularly in a chaotic setting like the one you described, often symbolize feelings of losing control in your waking life. The highway represents your life's journey, and the sudden chaos with the other cars may reflect external pressures or challenges that you are currently facing. The hydroplaning and spinning out of control could suggest feelings of vulnerability or anxiety about navigating your current circumstances.

The transition from the accident scene to the gathering with family and friends indicates a desire for connection and support during difficult times. The gray shadowy figures might represent unresolved issues or feelings of being overlooked or ignored in your life. Their presence suggests that there may be aspects of yourself or experiences that you feel are not fully recognized by those around you.

The realization that you were part of the accident and the subsequent sadness of your cousin and sister could symbolize a fear of being disconnected from those you care about, especially during times of crisis. The memorial at your apartment indicates a recognition of loss—perhaps not just in a literal sense, but also regarding aspects of your life or relationships that have changed.

Overall, this dream may be encouraging you to confront feelings of loss, vulnerability, and the need for connection. It might be helpful to reflect on any areas in your life where you feel out of control or unsupported and consider reaching out to loved ones for comfort and understanding. Embracing these emotions and seeking support can be a crucial step in navigating through challenges you may be facing.