Your power of attorney will be in effect according to the terms of its creation. In other words, you decide when the authority you have granted ends. However, if you do not use a durable power of attorney, it will end when you are incapacitated or die.
If the power of attorney is durable, it can end when you are no longer incapacitated and choose to revoke it. In the case of a springing power of attorney, it ends when you are no longer incapacitated.