“…Flexibility of the autonomic nervous system, indicated by alterations in both the sympathetic nervous systems (SNS) and parasympathetic nervous system (PNS) in response to stress, has been associated with better psychological adjustment (Appelhans & Luecken, 2006; Berntson, Norman, Hawkley, & Cacioppo, 2008; Thayer, Ahs, Fredrikson, Sollers, & Wager, 2012). While heightened SNS activation has been suggested to underlie the fight or flight response (Thayer & Lane, 2009), elevated PNS activation has been associated with increased concentration or a state freezing response under extreme stress (Bradley & Lang, 2007; Chou, La Marca, Steptoe, & Brewin, 2014; Hansen, Johnsen, & Thayer, 2003).…”