Ok... to try and make this as easy as possible:
There are two types of dissociation, the first is feeling spaced out, the second is having a flashback.
A flashback, you feel that you are literally back within the traumatic event, reliving it, not recalling it. This is not just thoughts or memories, you actually completely feel as though you are literally reliving it again / you actually begin to relive it again via behaviour.
People often confuse a flashback as being an intrusive recollection of an event, which is false.
Example Time
A car backfires, the soldier immediately goes to ground / tackles their loved one to the ground. Not a flashback, a learnt behaviour which is instinctual on hearing a shot fired.
A car backfires, the soldier immediately goes to ground / tackles their loved one to the ground, begins calling those around them names of their squad / section, begins calling in fire support, contact, starts firing and moving. That is a flashback.
A car backfires, the solider freezes, has immediate recollection of a traumatic event when a shot rang out. Not a flashback, a dissociative state.
A car backfires, the soldier freezes, has completely zoned out and in their brain, all they see is the war zone around them, feel it, smell it... imaginery people appear to them. This is a flashback, they are literally reliving a past event, placing the people, vehicles, etc within the image, completely oblivious to anything around them, not a memory, an actual full reliving of the event.