Hyperactive after a walk.

My 18 month parsons JRT loves his walks but goes crazy once back indoors for a while, chasing and trying to dig holes in carpets and chairs etc. Is he overtired, overexcited or just high on adrenalin?? He also tries to nip your toes and runs around barking - this can last a few minutes or longer and only after a walk. Any suggestions as to why this happens would be gratefully received.