The incidence of amnesia among romance novel characters appears a lot higher than in the general population. Lost identity is a convenient narrative device to make the characters start anew, and blank history provides beautifully for Big Secrets, Big Misunderstandings and Suspense. An amnesia story can be engaging drama. Unfortunately, the dramatic effect is often spoiled for me by the realization that the injury story is a complete fabrication. Many novels romanticize head injury and portray amnesia patients in a completely unrealistic manner.
Episodic memory means remembering one's own experiences and semantic memory stores facts.
Knowing Kennedy is a dead president would be semantic memory, remembering where you were when he was shot belongs to episodic memory. Most things we fleetingly sense or think about are forgotten right away but those that are more important or more frequent enter a long term storage. Later, when the information is recalled, one must somehow be able to access and retrieve this memory trace. The word amnesia is usually used to refer only to severe memory problems. Mild forgetfulness is generally not thought to be amnesia.