Dissociation: In psychology and psychiatry, a perceived detachment of the mind from the emotional state or even from the body. Dissociation is characterized by a sense of the world as a dreamlike or unreal place and may be accompanied by poor memory of the specific events, which in severe form is known as dissociative amnesia.

The term dissociation refers to the act of separating or the state of being separated.

Well, stress chemicals can cause headaches all by themselves... but I'd keep track of foods too or the like, to make sure it isn't irritated by allergies.