Yes, FIXATION is a Scrabble word!

Letter values in Scrabble US: F 4, I 1, X 8, A 1, T 1, I 1, O 1, N 1.

Is it a valid word?

FIXATION is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

an abnormal state in which development has stopped prematurely
an unhealthy and compulsive preoccupation with something or someone
the activity of fastening something firmly in position
(histology) the preservation and hardening of a tissue sample to retain as nearly as possible the same relations they had in the living body

Also: arrested development, infantile fixation.