Flashbacks are considered one of the re-experiencing symptoms of PTSD. As the name implies, in a flashback, a person may feel or act as though a traumatic event is happening again.
A flashback can vary in severity. A flashback may be a temporary occurrence, and a person may maintain some connection with the present moment. On the other hand, during a flashback, a person may lose all awareness of what is going on around them, being taken completely back to their traumatic event. Similar to a dissociative episode, during a flashback, a person may also lose track of time.