Terminal Lucidity is a phenomenon where someone who is completely out of it mentally (coma, dementia, schizophrenia, etc.) becomes briefly clearheaded just before they die.
From Scientific American:
Of 49 case studies of terminal lucidity (reported in a 2009 article in The Journal of Nervous and Mental Disease) the vast majority (84 percent) occurred within a week of death; 43 percent, in fact, transpired the final day of life.
They divide the phenomenon into two general classes, however. In the first subtype, "the severity of mental derangement improve[s] slowly in conjunction with the decline of bodily vitality." This occurs in some patients with chronic mental illness when their psychiatric symptoms become less pronounced, or disappear altogether, starting around a month before their deaths. Thus, the lucid periods emerge gradually, like clouds parting. The authors offer three Russian case studies from the 1970s as examples, all schizophrenic patients "without prior lucid intervals, living in seemingly stable psychotic mental states for many years." One man who'd been completely catatonic for nearly two decades allegedly "became almost normal" before he finally passed away.
In the second subtype of terminal lucidity, the authors tell us, "full mental clarity can appear quite abruptly and unexpectedly just hours or days before death."
