Quote Originally Posted by Brokedown Palace
What the hell, the chemicals in acid are totally gone from your system in under 30 hours..

Acid does not get stored in your spinal fluid.

Flashbacks are simply memories of a trip, which basically put you back in the mind set that you are tripping.
They linger quite a bit longer than 30 hours, if they didn't then the army wouldn't be able to test spinal fluid to determine if the person is capable of enlistment. It is for the reason of flashbacks that they disallow users of Acid into the military, at least in america.