I dug into the ANS not that long ago I came up with a few good strategies worth sharing:

1) ANS Reset Maneuver:
I came across this maneuver on a Ben Greenfield podcast and it involves 'unlocking' sympathetic stress. It is based on the theory that sympathetic stress directs blood flow to the arms and legs to compliment a literal sabertooth tiger fight or flight response. The maneuver is to be done once a day for 2 to 3 weeks. It involves laying on your back, head on flat ground (not a pillow), with your legs up on a couch. Imagine sitting on a chair and it being tipped backwards. You spend 30 minutes like this completely relaxed, no flexed abs or legs or any other muscle, complete relaxation. This works well with meditation. If you don't meditate effectively, listen to binaural beats or nature sounds. This will redirect 'locked' blood in the hamstrings, quads and biceps back into the gut and brain, thus resetting the ANS.

2) The adaptogenic herb ashwaganda.
This is commonly prescribed by functional medicine practitioner for adrenal gland fatigue. It calms the ANS by suppressing cortisol and promoting testosterone.

3) Activating the mammalian dive reflex.
This directly works on the vagus nerve related to the parasympathetic nervous system and is another biohack based on evolutionary thought and proven by science. When your face is submerged in cool to cold water, it increases vagus nerve tone and slows your heart rate. So, when your anxious or approaching bedtime, fill a large bowl with cold water and dunk your face for 30-40 seconds. Thats it. That will activate the mammalian dive reflex. Keep the dunk times short so as not to risk drowning. When my sleep sucks, I do 2 sets of this before bedtime.

4) Breathing Exercises.
Box breathing can calm the sympathetic nervous system. In fact, Navy Seals are trained to do this prior to missions. It is as easy as a couple minutes of 4second inhale, 4second hold, 4second exhale, 4second hold with zero force and relaxed muscles.

5) Meditate.

Hope these help

Hains