You have this comet trail of your own lived life, sparks from which arrive in the head all the time, whether you want them or not - life has been lived but it is still all going on, in the mind for better and for worse.
The idea that memory is linear is nonsense. What we have in our heads is a collection of frames. As to time itself-can it be linear when all these snatches of other presents exist at once in your mind? A very elusive and tricky concept, time.