not to be vary this seem to be breath holding spell in your child .
but i want to know one thing weither your child had episode only during climbing stair only or this episode used to occure any time . second thing i also want to rule out convulsion
in children like infantile spasm . GET an EEG done to rule out convulsion .
breath holding spell did not lead to mental retardation .
give iron to the child . this will decrease frequency of breath holding spell.
thanks . hope you have found your adequate answer