It definitely sounds like a disassociation response. Yes, your body can still respond to traumas after-the-fact. Have you had therapy for your trauma?

Exposure therapy is sort of what you are accidentally doing, by watching movies that will trigger your past trauma. That can work to your benefit, as long as you are aware of it happening.

If your exposure and disassociation is accidental and spontaneous, then yeah, I think a therapist could help you develop coping skills to use as a response to these moments of disassociation.