Many a times it feels that certain events happened just recently, even though they had happened very long back. It is hard to believe that they belong to the far past.
On similar lines, it feels that some events occurred ages back, though they are just a few weeks/months old.
Mostly those in the former category were happy ones and those in the latter the disturbing and not-so-happy ones.
Perhaps there is no mystery in this mysterious feeling. It may be the inherent tendency of us humans to shroud the unpleasant and cherish the pleasant. Forgetfulness is not entirely useless.