Brief Answer:
I don't believe so...

Detailed Answer:
Hello,

I don't believe it's the action of the vagus nerve, which controls some parasympathetic actions. Although salivation is indeed one of its actions, the parasympathetic system is active when we rest (when we start to feel sleepy after eating for example). When we engage into physical activity the sympathetic system (which has the opposite effects) is very active. Having excess saliva after physical activity is strange. We do get some saliva when exercising but it's not the watery type that we get when eating. Actually this saliva is expected to be sticky, not watery. This little extra saliva helps to keep the mouth moist during exercise (sympathetic). The water-like saliva helps to swallow and digest the food (parasympathetic).

Regarding nausea, it can be considered normal after very strenuous and protracted activity (perhaps along with a sensation that the head is going to explode, etc). It's not common with less intense activity though.

Since you've been having both symptoms for all your life then I'm sure it's nothing serious but I don't have any good explanation (documented in medical literature that is) or any solutions to your problem. There are drugs to reduce the symptoms but they'll probably reduce your exercise potential as well and it's not very wise to take drugs for something that seems to be 'normal' for you.

I've assumed for my answer that you don't take any drugs. If you do, please check their side effects or let me know their names and I'll do it for you.

I hope it helps!
Kind Regards!

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