Overstimulation of heart by vagus nerve, decreasing rate of cardiac contraction drop in cardiac outflow compensated by peripheral vasoconstriction to increase blood flow to brain (vasovagal response). The sudden fall in blood pressure sudden brief loss of consciousness full recovery in several minutes
Cause – some sort of stimulus – eg pain; grief; anxiety; fear; emotional events; standing for long periods; sight of blood or needles.
Prodrome dizziness/light headed; yawning; nausea; pale, cold, clammy skin; may feel hot; anxious; dimming of vision; tachycardia
Then collapse; loss of consciousness; bradycardia; may have abnormal movements
If unconscious place in lateral stable position; raise legs if possible
If conscious lie flat; raise legs if possible
If heat syncope loosen clothing and cool by fanning
May recur if stand up within 30 minutes