The actuality of it is really that LSD is stored in the fat cells of your body. Over time, as these break down, small amounts of LSD may be released back into the bloodstream causing a breif hallucinogenic flashback. I've had a few (did a bunch of LSD in the 70's-90's), but I'm pretty skinny, so I really don't have very much fat at all, let alone a significant amount for extra LSD storage.

Bummer, but that's the way the wee wee drizzles.