Fear.
Fear is ruled by Saturn, Neptune.  The octaves of thought perception: Mercury and Uranus also factor highly (anxiety).
Strong placements of these planets, hard aspects to them (especially Sun/Moon) will indicate a tendency toward fear (difficulty).  Hard aspects to the 8th or 12th house will indicate (repressed) fears. *

Mars strong in good aspect indicates fearlessness – the same holds true for Pluto, the higher octave of Mars, and aspects to it.

What is the primal baseline ?
Fright.
1. Fight
2. Flight
3. Freeze

What actions are taken in a fearful moment depends on the natal chart.*
As well as progressions of said natal chart and transits to both.  Planetary energies will lend support and confidence or add to stress and panic to what is present in the natal.

Being a Capricorn rising (Saturn-ruled) with Mercury at high noon, Uranus conjunct Sun and Moon opposite Neptune most highly aspected with squares to the 8th, I am familiar with fear.  I have been working on it for years…now it is more akin to caution.  I work to keep my mega-reckless Mercury/Uranus/Sagittarius energy in check.

I will not fear.
Fear is the mind-killer.
Fear is the little-death that brings total obliteration.
I will face my fear.
I will permit it to pass over me and through me.
And when it has gone past I will turn the inner eye to see its path.
Where the fear has gone there will be nothing….only I will remain.
Litany against fear, DUNE

Living a life full of fear, trauma and flashbacks often leads to post-traumatic stress disorder (PTSD) symptoms outlined here and here.
How to begin healing PSTD here.  Differing forms here. 

Hard aspects (see above) to these planets may indicate fear and/or trouble involving:
Sun – life, father, children, that which you create
Moon – home, family, mother, women, emotions, public
Mercury – thinking, speaking, neighbors, children, driving
Venus – love, money, relationships, bonds, disharmony
Mars – aggression, men, competition, leading, fire
Jupiter – wide outdoors, flying/foreign, stupidity, clergy, judges
Saturn – small spaces, age, falling, breaking, caves, change
Uranus – cages, boredom, electrics, abandonment (no ground), heights
Neptune – that which is hidden/confusing, lies, lack of art/empathy, noisy crowds
Pluto – superficiality, transparency, apathy, peacefulness

Keep in mind the hard aspects ensure growth ala friction.  Trines and sextiles are fabulous grace periods but not particularly keen on forcing flowerings.  Just sayin’.

May you face your fears and remain
Gneiss Moon