With no special effects, it nevertheless bared moments of terror.
Michael, its central character, is a family man who gets involved in testing anti-depressants -- and keeps doing so in secret after testing is halted due to violent side effects.
No longer satisfied with life as it has been, he begins to make life for his loved ones impossible, in what he thinks is a quest for control.
Set amid magnificent landscapes, with strong acting, "Fear Me Not" comes over as feeling very cold, with sometimes violent scenes.
From across the Atlantic, "Frozen River" -- already screened at the Sundance film festival -- is the first offering from director Courtney Hunt.
Its heroine Ray Eddy is on the point of buying her dream home when her gambling husband leaves the family deep in debt.
Desperate to make ends meet, she accepts an offer from a Mohawk woman to smuggle illegal immigrants across a frozen river in winter from Canada into the United States.
Bonds of friendship emerge between the two women, who face similar family and economic hardships and together go through testing times.
Happiness and joy have so far been missing from the official competition in San Sebastian, which continues through September 27 with US director Jonathan Demme overseeing the jury.
On Friday, festival goers were treated to "Two-Legged Horse" from Iranian director Samira Makhmalbaf, a hard-hitting picture well received by the critics.
Fifteen films are in competition, including "Bi Mong/Dream" from Kim Ki-Duk of South Korea, "Genova" by Britain's Michael Winterbottom, or the latest offering from Japanese director Hirokazu Kore-Eda, "Aruitemo, Aruitemo/Still Walking".
Last year the jury, chaired by US writer Paul Auster, awarded the Concha de Oro (Golden Shell) award to Hong Kong-born US director Wayne Wang for his drama "A Thousand Years of Good Prayers".