Answer:
If you suffer from this, you might wear a wig
What is filled with air and sometimes a gas, tied to a string and often seen on your birthday?
What has a neck and no head, two arms but no hands?
What can you hold in your left hand but can never hold in your right hand?
What has roots that nobody sees, and is taller than trees. Up, up it goes, and yet it never grows.
Of these things - I have two. One for me - and one for you. And when you ask about the price, I simply smile and nod twice.