All highly sympathetic persons who have closely accompanied beloved friends through a great sorrow have known something of this subsequent feeling.
The close connection and continuity between normal and abnormal states of mind is illustrated in the fact that in insanity the illusion of taking past imaginations for past realities becomes far more powerful and persistent.

Abercrombie (_Intellectual Powers_, Part III.sec.iv.

Sec.
2, "Insanity") speaks of "visions of the imagination which have formerly been indulged in of that kind which we call waking dreams or castle-building recurring to the mind in this condition, and now believed to have a real existence." Thus, for example, one patient believed in the reality of the good luck previously predicted by a fortune-teller.

Other writers on mental disease observe that it is a common thing for the monomaniac to cherish the delusion that he has actually gained the object of some previous ambition, or is undergoing some previously dreaded calamity.
Nor is it necessary to these illusions of memory that there should be any exceptional force of imagination.

A fairly vivid representation to ourselves of anything, whether real or fictitious, communicated by others, will often result in something very like a personal recollection.