According to a recent study conducted at Northwestern University and published in the Journal of Neuroscience, artificially creating a "fight or flight" response might increase your ability to remember as well as decrease your reaction time.
In the study, researchers monitored the breathing patterns and brain activity of volunteers who were shown faces depicting either fear or surprise, and asked to identify the emotion depicted as quickly as possible.
Much to the researchers' surprise, people who took short breaths through their noses reacted more quickly and remembered more of the faces that they'd been shown. As the study noted:
"Behavioral data across three experiments and 62 participants demonstrated that respiratory phase and route have a significant influence on emotion discrimination and recognition memory. Independent groups of healthy subjects were better able to recognize fearful expressions, and were better able to retrieve visual object memories, when target stimuli were encountered during nasal inspiration than during expiration."
Turns out that breathing quickly through your nose is a genetically-programmed human physiological response to anything that seems threatening--part of the classic "fight-or-flight" reaction.
Apparently, the fast breathing floods your bloodstream and consequently your brain with extra oxygen, making it temporarily more efficient. Interestingly, this effect only wlork if you inhale through your nose. Mouth-breathing doesn't cut it:
"We also found that the route of breathing was critical to these effects, such that cognitive performance significantly declined during oral breathing. Importantly, the effects of nasal breathing on cognition were sustained even when subjects were asked to hold their mouth open, helping to control for attentional confounds that might have arisen during the oral breathing experiment."
Of course, this is a relatively small study and has yet to be confirmed by additional studies. Still, since it costs literally nothing to try the method out, it's probably worth a shot.