Is boredom a physical state, a mental state, or both?

I’d consider it a mental state. But there are analogous physical conditions.

Mental, but can manifest in a ton of physical ways, of course. Agitation, restlessness, drowsiness, fidgeting, cabin fever, etc…

Mainly a lack of stimulation.

There’s a fine line between boredom and loneliness*. And loneliness registers itself in the same receptor cells in the brain as physical pain. (Cite).

*from dating experiences where I encountered, or was myself, a person who was there to be either entertained or validated: not always a clear line of demarkation

It is the absence of Zen.

Is it also the presence of not Zen?

Familiar as I am with boredom, I will say that for me it starts as a mental state and if left untended, soon becomes a physical state. “I’m bored, I don’t have anything to do” will, in a matter of hours, become “I don’t feel like doing anything.” It’s a downward spiral for me. And I like the idea that it is related to loneliness, which never occurred to me, but I agree. If I even had someone entertaining to call on the phone, the boredom would be relieved.