When I have the mod installed, my character's head keeps moving up and down rapidly.

It’s a big with Performant

You need to go to the config file of performant and set fastCollisions on false.

Just found alternative fix for this issue yesterday.

Basically go to config file of Camera Overhaul and set verticalVelocityPitchFactor to "0.0". It should be like this

Edit: Oops, I have accidentally shown my bottom toolbar of my PC, reuploaded the new one