Brain waves can be measured with an EEG
Feeling relaxed is usually correlated with a sufficiency of alpha waves, and conversely an anxious state of mind with an absence of alpha waves. A 2018 study found that those people experiencing an anxiety trait have beta waves that overpower their alpha waves, which over time accumulates into feelings of constant stress.
However, researchers of Psychology and Physiological Science at Ball University found that having too many alpha waves in the resting state can also be equally disruptive. They found that highly anxious subjects showed more alpha wave activity (were essentially more relaxed) in the resting state than less anxious people. However, during a specifically designed so-called "Eriksen-Flanker Task" to make subjects alert and focused, both groups showed similar alpha wave activity. Seemingly counterintuitive, this observation seems to imply that alpha waves in a highly anxious person suppress the processing of external stimuli / information.
Ward, Richard T.a; Smith, Shelby L.a; Kraus, Brian T.b; Allen, Anna V.a; Moses, Michael A.a; Simon-Dack, Stephanie L.a Alpha band frequency differences between low-trait and high-trait anxious individuals, NeuroReport: January 17, 2018 - Volume 29 - Issue 2 - p 79-83
