I agree with you, @Amyjay and @amandalouise, that flashbacks is not simply the same as re-memebering something you had forgotten about, but I think you can still have flashbacks about something you had forgotten, and the flashback doesn't necessarily include everything you sensed at the time. Thus it may be hard to understand to understand what it comes from, and what exactly triggers it. You can have flashbacks to something you felt emotionally or physically as a young child, for instance.