Some of the best advice I read was that babies are like us - sometimes you feel energetic and feel like kicking up your heels and sometimes you just want to laze around. I often find that if bub has a quietish day she makes up for it the next.

Also, the position has a lot to do with it. In mid-pregnancy when there is still plenty of room to turn around and upside down and every which way, bubs may be kicking and punching more towards the back of your uterus which you won't necessarily feel.