First Person Camera Rotation 360 degrees on all axis

Hello,

I wondering how to create a camera that can rotate at 360 degrees on all axis, just like a spaceship. I di several tries but I still have the same problem : when I'm upside down, Z-Axis rotates to 180 degress without asking anything and controls are reverted.

I tried to use the Unity FPS Controller Mouse Look Script. I also used a Mouse Torques script fron Unify but it's very unstable. I also tried to understand the problem with this Simple Smooth Mouse Look script with the same problem and no results.

I'm, at this moment, working with the Simple Smooth Mouse Look script on my camera, trying to solve this. May someone help me to understand why this behavior occurs and how to change it just like I want ?

Thanks in advance.