I've had nystagmus in my left eye for decades. It only causes a problem with my ability to track a fast moving object like a baseball . From what I've learned, Nystagmus is an eye movement symptom, not a stationary symptom. They diagnose it by having you follow an object as it is moves from side to side. A normal eye will follow it smoothly. An eye with nystagmus will jerk as it moves from side to side. There would be no nystagmus symptom when looking at a stationary object with the head still. If you move your head while trying to stay focused on a stationary object, the nystagmus would manifest.

Some will use the term nystagmus to define other eye movement disorders.

One can have nystagmus and other eye movement disorders at the same time.

You may need a behavioral optometrist to assess your vision. This sounds more like your left eye is hunting to line up with your right eye. This is a convergence 'like' issue where the two eyes are not lining up the image so the brain can stitch the two images into one. Some terms are strabismus. accommodation/vergence disorders. These disorders can cause dizziness because a large part of balance issues are visually based.

It sounds like you need to find someone who can help you with the ear popping and fullness issues. Those symptoms are likely easier to treat than strabismus, nystagmus (rarely treatable) and the other eye movement disorders.