Hypoglycemia: Vasovagal symptoms occur more readily when the blood sugar is rapidly dropping and even more so when it is low (hypoglycemia). This may be because the brain is receiving an independent insult in that not only is it losing perfusion from autonomic dysfunction, but was already starving for glucose. It’s also possible that the vagus nerve becomes all the more dysfunctional with rapid glucose drops. One consequence of this is that autonomic dysfunction seems to happen in slender people more possibly because they have no fat reserves from which to synthesize new glucose when hypoglycemic.
Dehydration: Understanding the details of autonomic dysfunction thus far, its not surprising that having insufficient fluid available to fill the tank would be a problem. Likewise, dietary salt, which pulls fluid into the blood stream, is also important in being able to fill the tank.
Sleep deprivation: Being chronically tired also seems to increase the symptoms associated with vasovagal syncope. This could also be an independent insult to the brain or the effect may be through a change in vagal activity.
Growth Spurts: As mentioned before, the vagus nerve just seems to have trouble adjusting to new height.
Excessive Exercise and Exercise deprivation: When a healthy young person finds themselves in a period of sedentary life, the symptoms of autonomic dysfunction often appear or worsen. Just as their muscles lose tone and strength from inactivity its likely that so too do their blood vessels leading to inappropriate vasodilation. However, excessive training can also lead to increased dysautonomia. Training enhances vagal tone (makes the vagus nerve even more active and twitchy). It also increases the volume and stretchiness (compliance) of the tank. Finally, its likely that training leads to exaggerated fluid and electrolyte shifts during exercise and recovery that knock the body off its normal homeostasis (balance). In my experience, it is the athlete who has chronically intensely trained who then turns sedentary to pursue academics more rigorously, who is most risk of onset of dysautonomia.