You always remain YOUR OWN Level 0.
You are the level 0 of your own personal 16 level network below you.
It means you are the 'top' of your own 16 level network.
For example; the people you refer into your Level 1 are also their own level 0 of their own 16 level network below them.
Each affiliate has 16 levels below them.
Your level 1 affiliates see you titled as 'Sponsor'.
Your Sponsor sees you as their level 1.
For more information and a diagram see, your back office - Downline menu