Is it possible for someone who has lost their personal identity and past memories, to get overwhelming deja vu experiences?

Yes, it's possible: Depending on the cause of the memory loss, these could be dissociative flashbacks. That means the memories are still there somewhere but a defense mechanism called dissociation is keeping them from waking memory. If the problem is not physical, a psychologist who specializes in this would be helpful in assisting you in answering this and maybe regaining some of your identity.