Humans, like all life, are sensitive to their environment. Human and animal individuals can be triggered into impulsive and even violent activities from spikes in serum serotonin. Serum histamine level is directly proportional to environmental allergen levels producing dreaded seasonal allergic symptoms. But serum serotonin level, or the control of the level, is inversely proportional to serum histamine levels. Examples are presented where analysis over time of stock buying, as measured in the daily closing level of the United States stock exchange, shows a seasonal “J” shaped pattern that correlates with serotonin falls and spikes (histamine spikes and crashes) induced by the rise and fall of environmental allergens. A logical predictive strategy is thus presented where, excluding very large shocks like wars, market players could “buy low” an exchange-traded fund (ETF) i.e., indexed “stock,” every fall season (between August 25 to October 5) and then subsequently “sell high” (between October 17 and November 10) as increased serotonin in the aggregate population leads to the increase in impulsive and speculative (over-confident) stock buying before “normalizing” around late November.