vasovagal syndromevasovagal triggersdefine vasovagalvasovagal syncope treatmentneurocardiogenic syncope syndromeneurocardiogenic syncope diagnosisvasovagal syncopal attackrecurrent vasovagal syncopemalignant vasovagal syndromevasovagal syncope pathophysiologyvasovagal syncope diagnosisvasovagal syncope exercise