Anxiety is caused by the Illusion of Separation.

Anxiety is caused by Self-illusioned separation (in the understanding that Self is one without a second). The illusion of separation causes almost all if not all anxiety (and certainly most conflicts). Separation from what? Separation from One's True Self; from knowing 'Oneself Itself Is' and that any otherness is illusory. Oneself is the singularity! So what is Oneself? That which eternally is; it is commonly known as God. Oneself itself is the eternal One physically manifesting itself as manifoldness; but by doing so purposely deludes itself, its manifoldness, to forget it is in reality itself. Unbelievable right? The illusion of separation simply exists so Oneself could experience love and I accomplishes this through the mechanism of its self-illusioned separateness (and all this simply to escape aloneness). Oneself is you, it is I, it is all the 7.7 billion people (plus a few hundred billion-plus other species and counting) who have no clue they are in reality One and the same. All is I AM; all is Oneself simply looking for companionship and love. What we can do as humanity is to align ourselves with our (I's) primary purpose and come together as one for we are and always will be.
~ Wald