My 9 wk old puppy shakes in sleep?

I just got a 9 wk old english mastiff today and hes adorable :) However, i've noticed that when he has been sleeping for a long time, (deep sleep) he starts shaking, not shivering, but like he'll shake his head all around and he'll move his paws and kick his feet. Im mostly scared about the head moving. He like swings it around while hes sleeping! Should i be concerned? Anything to prevent this?