Dissociative amnesia is a type of dissociative disorder. There are multiple types of dissociative amnesia.
Its primary symptom is the sudden inability to remember important personal information or event, not attributable to drugs, medical illness, or dementia. Tends to be short-lived and to remit spontaneously, and it's hard to intervene on.
Fugue is a type of dissociative amnesia with flight (fleeing from regular life), new identity, confusion. It's very rare. Typically, there will be a missing person report, and the missing person will be found living in a completely different place with a new identity. Confronting the person usually causes them to realize their original identity.