Rubbing the top of a birds head a bad thing?

I have a parakeets who's wings are clipped... shes a girl and really feisty. If you've ever rubbed the top of a baby chicks head... they normally fall right to sleep. Everytime I pick her up she squaks and tries to bite me... I tried rubbing her head and it puts her to sleep until I stop rubbing it... she is a full grow parakeet... will this harm her? Or does it just make her sleepy? She seemed comfortable with me after I rubbed her head.