1. Humming
You know all of those people you used to think were "new age" because they would sit quietly and repeat the "OM" sound? Well, it turns out they are on to something. Because the vagus nerve is connected to your vocal cords, systematic humming can stimulate the nerve.
2. Speaking
Likewise, people who speak more are more likely to be able to raise their vagal tone as talking is done through the vocal cords. Singing and laughter in general will also do the trick.
3. Wash your face with cold water
A splash of cold water does seem to stimulate the vagus nerve. Whenever your body is required to adjust to the cold, your fight-or-flight (sympathetic) system declines and your rest-and-digest (parasympathetic) system increases.
In other words, any kind of sudden cold exposure will increase vagus nerve activation. You can achieve this by either dipping your face in cold water or take a cold shower.
4. Breathing deeply using your diaphragm
Breathing long, deep breaths from your diaphragm can stimulate and tone your vagus nerve.
5. Yoga
Research shows that yoga, along with breathing practices, can significantly increase your vagal tone.
6. Meditation
According to a 2010 study, people who meditate regularly and think more positive thoughts tend to have better vagal tone.
7. Increase Good Gut Bacteria
While there are countless benefits to increasing the healthy bacteria in your gut, surprisingly, this also helps to create a positive "feedback loop" through your vagus nerve and thus increase its tone. Probiotics are a good source of healthy bacteria.
In Summary
All of the above methods are beneficial to your overall health simply for the fact that they also help reduce stress, which is a major factor in disease, but also knowing that you can help improve your vagal tone, and the specific issue of inflammation, is a powerful tool.
Add these simple tips to your daily routine and see how much better you feel in a relatively short time.