Excerpt from Natural Baby and Childcare

Arnica montana (Arnica) Arnica is a plant that grows high up in mountain slopes where one could easily get injured in the steep terrain.  Hence, Arnica is an excellent treatment for trauma, Arnica is the medicine needed most often in my active household, and it works without any side effects.  Arnica is the only remedy that I use routinely during birth, as well as during the post-partum period. I also use it for newborns who are bruised after birth. Arnica has no contraindications, and is safe for newborns and nursing mothers. Arnica in strong potency (200C or 1M) is used for major injuries.
 
Arnica is useful for:

Mind:

Restlessness
Bed and chairs feel too hard.  Difficult find comfortable position
Says there is nothing wrong, even when seriously ill.
Desires to be alone
Irritable
Body feels as if bruised

Body:

Bruises, swelling and muscle soreness
Sprains, strains and concussions
Injuries and bleeding from trauma and accidents
Jet lag (with muscle soreness)
Falls and blows
After-surgery swelling (plastic surgery, caesarean section, dental procedures)
Over exertion from lifting, sports or work
 
Complaints are better: alone, lying down outstretched or with the head low

Complaints are worse: touch, jarred, cold and damp weather, lying on injured part,