The ‘ripples’ of dysautonomia, often vasovagal phenomenon, can occur at what seems random times but there are certain circumstances when the symptoms are more likely to occur. Here are some:
One very com- mon circumstance is with orthostatic changes (changing positions from lying to sitting to standing). An adolescent may stand up quickly but the withdrawal of vagal tone needed to allow the heart rate to increase and blood vessels to constrict does not happen quickly enough and a head-rush ensues. Sometimes this is followed by black-out vision and even syncope after several steps. This seems to be more exaggerated if the person was lying for a long time, say, watching TV or sitting and doing homework for hours.
The problem may not be confined to orthostatic changes but to other situations where excessive vasodilatation occurs. Common times that vasovagal symptoms occur includes stepping out of a long, hot shower, having one’s hair combed by another, standing for a long time in a hot place, and having a tight constrictive collar.
These are times when the body suddenly dilates the small vessels that send blood out to the skin. This effectively increases the tank size rapidly and blood pressure is lost centrally. Again, this affects the organs sitting highest in the tank – the brain being the highest.
Other common times that vasovagal symptoms occur is when the vagus nerve becomes over-stimulated by other means. Being that the vagus nerve is part of the bigger parasympathetic nervous system, when other parts of the parasympathetic nervous system are activated, the vagus nerve sometimes gets dragged into it. Urination and bowel movements requires activation of the parasympathetic system and so sometimes vagal tone increases and light-headedness occurs when one stands up from the toilet. Nausea is a parasympathetic action in the gut that also spills over to the vagus nerve so fainting is a common outcome in circumstances involving nausea. These components are probably all tied into the phenomenon of squeamish folks fainting at the site of blood and gore.