How can something intolerable be understimulating?

When I'm in a room where you're ostensibly supposed to be listening to someone talk -- a lecture, a sermon, etc. -- I can't properly stop listening. So if the speaker is really boring, I will try to zone out, but usually with very little success. It combines the worst parts of being with other people with the worst parts of being alone, for an experience that is both understimulating and agonizing.

I once had to sit through a two-hour Southern Baptist church service. There was one guy who delivered a long, rambling, over-excited monologue about "casting out demons and devils", sounding exactly like a random street lunatic, and then another guy who spoke in a more sedate tone for about an hour on how evolution is false, society is being corrupted, and how "we did not come from monkeys!!". And then there was one man whose job appeared to be simply to sit in a chair next to whoever was speaking and periodically agree with whatever was being said. Whenever there was a pause, this guy would jump in with a "YES!" or an "AMEN!". I think the funniest thing that happened was when somebody mentioned Jesus and then stopped to inhale, and this guy blurted out "THAT'S HIM, THAT'S HIM!!".

At first it was morbidly fascinating, in a mentally painful sort of way. But as time wore on, it just became excruciatingly boring, as they covered the same ground again and again, as if their target audience was suffering from profound mental retardation. I tried to think about something else to escape from the dull horror of my surroundings, but the preacher's delusional ravings just kept impinging on my train of thought, inescapable.

So, yes, it's entirely possible to be intolerably understimulated. (I enjoy meditation, though. It's quiet enough that I don't get bored, if that makes any sense.)