ive had my cockatiel 7 years so know his moods quite well by now,,, he was hand reared and ive had him since he was a little fluff! 1 thing i have learnt with birds (i had a grey too) is sometimes their is no reason for their behaviour!!! sometimes they are just moody!!! its what they do lol its what gives them character, i bet yours will snap out of it as quick as it all started