Wandering in a conservatory recently, I became nostalgic for the time I used to visit Kew Gardens quite frequently as it was just a 20 minute train ride away from my home.
It occurred to me that perhaps there is a conservation law of recall. Perhaps you can only recall things so many times. Perhaps, just as with Computer Solid State memory, and with rechargeable batteries, human memory can only take so many "read/verify/rewrite" cycles - after all, as we now know, memory is not a vault. It is active, and conserved by being used. However, it is not immutable - usage makes it alter (see the Julian Barnes novel A sense of ending for a very fine evocation of this.
So entropy applies. This means that too much nostalgia will lead to dementia. Perhaps the rise in Alzheimer's is not really due simply to people living too long, but is a side-effect of having the ability to recall so much so easily at the tips of your fingers on the interweb. Perhaps nostagia is killing the past, a piece at a time - perhaps the Eternal Sunshine of a Spotless Mind is not a fiction, but an epidemic.