Sometimes my baby is shaking head back and forth. some situations I observed are: 1. right after waking up from sleep 2. when he comes into crawling position from sitting position(not every time, only few times) 3. when we make hime sit after holding him(not every time, only few times) 4. sometimes while playing 5. when someone waves him bye, he shaked his head 6. when we are in deep conversation, sometimes he is silent and listening, then he shakes head etc .. he is doing it from last 9 days. he is having cold and does not have any fever. he is completely active and reaching all the milestones on time and his weight is 11.5 kgs. please let me know if this is normal or not?