Can someone fill the gaps I have regarding what exactly changes from one state to another during a particular electromagnetic circle?
First, let's assume that this is a pure magnetic field characteristic. Starting from point $0$ it begins gradually to increase its magnitude until it eventually reaches its maximum, then starts to decrease in value and reaches a point $0$ or half circle ($180$ degrees) and this is where my confusion takes place. How come the magnetic field can have a negative value? It just doesn't makes sense to me, something either does not exist (point $0$) or does exist (somewhere above $0$).
My confusion gets even worse when it comes to comprehend the electromagnetic dependency.
Two separate fields perpendicular to each other start at point $0$, gain some magnitude over time and reach their amplitudes, then start to decrease in value and reach the half circle point $0$ ($180$ degrees), Then they both pass to their second half circle (below $0$) up to $360$ degrees.
So, what I am really asking for is general explanation about what is happening. I am aware of the mathematical point but I lack real, essential understanding of how this actually works in reality. We take many classes full of formulas, diagrams and regular exams but I feel that I am missing the bigger picture. As Richard Feynman once said, there is a big difference between knowing something (memorizing) and actually understanding it, and I feel that I merely know this, rather than understand it. I am looking here for a deep fundamental understanding, not a textbook definition.