I appreciate your interest as an individual and as a writer and therefore find your curiousity and enthusiasm a great positive. I would disagree that many people with PTSD have normal lives, though it varies greatly from individual to individual.
I would say there is more than just flashbacks, memories and nightmares - especially from the storytelling perspective - many books without prologue would seem to have a character that experiences that. It would be important to realise that there are different forms of flashbacks and more importantly a flashback isn't just remembering a memory it is re-experiencing the event that caused the memory.
Flashbacks vary from emotional/individual sense flashbacks to full-body flashbacks where the individual completely smells/hears/tastes/feels the things that happen. In some cases it results in a complete blackout, whereas others there is an awareness of the real world involved, both are terrifying for different reasons.
It's the anxiety and fear, shame and guilt (not just for abuse victims, many vets seem to be deeply ashamed of the social stigma), hyper vigilance, the sometimes exhausting level of frustration at oneself that in some cases dissociation and then there are things that are related to that type of trauma - job related - army/naval, police, fire-fighter, ambulance; physical abuse; sexual abuse, ritualistic abuse, emotional abuse, extreme neglect. The age that the abuse happened, whether or not it is sustained/repeated abuse, if it is complex in nature, the nature of the abuser (care-provider/position of authority/school peer). And then specific, individual and unique stressors and triggers relating to the nature of the trauma and the persons perception of that trauma.
Then there are external factors such as social stigma, social isolation, the varying degrees of medical acceptance of PTSD (and depending on the trauma, Dissociation) as a disorder and how much it affects people. Whether there are no other issues such as the aforementioned dissociation or any personality disorders or substance abuse.
Some people with PTSD can hold down jobs and wouldn't be without one, enjoy social company and function fairly normally unless triggered and even then can regain a sense of normality far faster. Others can't leave the house, are fearful of people to the extent that just being seen/looked at is painful, have frequent flashbacks and poor sleep, it would be impossible for them to have a job, even from home because of the stress of it. There is an enormous amount of variation, as varied as the trauma and individual.
I presume you will elaborate later on and I will not go any deeper into all of this now, I just wanted to say there is more than the flashbacks/nighmares/memories. But as to the portrayal of flashbacks from a reader who has encountered flashbacks in novels (as well as TV and Cinema), they are typically portrayed very differently to how they are experienced in PTSD. As a writer myself, it is a tool I would personally never use to simply fill in some back story or out of relation to PTSD because I believe a memory however vivid is not the same as a flashback.
Good luck and I hope to be of more help and see the other responses you get.
