Question

how was this vile nervous fit, for such i now persuaded myself it was, to be conquered? i determined to force myself not to look at the painting but to undress quickly and get into bed. i began to undress, but in spite of every effort i could not keep myself from stealing a glance every now and then at the picture; and a glance was now sufficient to distress me. even when my back was turned to it, the idea of this strange face behind me, peering over my shoulder, was insufferable.
how does the excerpt exemplify gothic fiction?
by revealing an unhinged psychological state
by describing a scene of blood and gore
by depicting the triumph of reason over the irrational
by illustrating the confused plans of the narrator

Explanation:

Gothic fiction often explores psychological states of unease and instability. The narrator's inability to stop looking at the painting, the distress from the idea of the face behind them, and the "nervous fit" all show an unhinged psychological state. There is no mention of blood and gore. The narrator is not showing triumph of reason (they are distressed by the irrational idea). The confused plans are not the key Gothic element here - the psychological turmoil is.

Answer:

by revealing an unhinged psychological state