Vitamin B6 deficiency is associated with microcytic anemia, electroencephalographic abnormalities, dermatitis with cheilosis (scaling on the lips and cracks at the corners of the mouth) and glossitis (swollen tongue), depression and confusion, and weakened immune function [1,2]. Individuals with borderline vitamin B6 concentrations or mild deficiency might have no deficiency signs or symptoms for months or even years. In infants, vitamin B6 deficiency causes irritability, abnormally acute hearing, and convulsive seizures [2].
I think if you are low on B6 you will definitely notice it. If your levels of B6 are fine, then you probably won’t notice a difference.
How will you know you are deficient in B6?
From (US) NIH fact sheet:
Blood test to check for nutritional deficiencies