Does every person who suffers from PTSD experience flashbacks?
No. Flashbacks are actually not as commonplace as you might think. Re-experiencing is far more than just a visual event for many.
Re-experiencing can be produced by a familiar scent, a familiar sound, a familiar energy, or a familiar sensation. All of which are not necessarily connected to a visual image. The brain remembers in many ways
For those that do experience flashbacks of visual images, it can be an all-consuming mind/body experience that rattles you to the core. As I have said a number of times, it doesn't matter what your traumatic event was, if it frightened you and threatened you with mortal danger or threatened the life of another, your brain logged it for processing at a later date. Those images can be frightening when they start running like a movie reel in your head because the movie feels like it's happening right now.
I have met some that have not experienced direct trauma to themselves, but were in a position of being fearful of the mortal implications to another human being. This is equally as traumatic and can wreak havoc on the fear of something like that happening again. Some will wake up at the same time each night thinking something is wrong and be awakened in a panic. Some have night terrors where they re-live getting a terrifying phone call or are afraid to drive down a street where they saw someone get into a terrible accident. It's possible someone knocking on the front door causes fear because they received bad news about someone they know. This is all about re-experiencing something traumatic that happened and it's really about feeling, not necessarily seeing.
Post-traumatic stress is about the human condition. We are equipped and wired to feel. When we are put into a position where we are afraid to feel, this is where the real battle begins.