Your baby might start shaking his head out of the blue and can look really worrying and strange. But you should just relax and enjoy this new skill your baby has developed. His head with his strong motor and muscle development, will no more be wobbly even if his body sways.
What you need to know
At this age, your baby starts shaking his head as a part of learning to get control of his body. He may be imitating you or may have discovered he gets lot of response from you when he tries this trick. This of course, is the real sit-back and enjoy season, nothing at all to worry about.
Howevrer, head-shaking may also indicate an ear-infection! If you think your baby has had a cold, is running a fever, is less active than the usual or may have an infection, it is worth checking out. In general, head-shaking is just another interesting stage, but worth checking for any infection or sign of Autism in rare cases. Your baby can also shake his head when he gets tired, as self-soothing. Sometimes he also shakes his head until he falls asleep.