she started yesterday, she'd just finished a breastfeed and she lifted her head back to see something and she started shaking her head, rather rapid shaking, only lasted about 5 seconds but ive never seen her do it before, shes my 4th and non of my others have ever done anything like it, i know it doesnt sound much, but it looked very odd, any ideas? am i just being a worrier? btw she's 5 months.