There’s nothing dictating that your brain needs to have one decisive opinion. It’s just a bunch of nerve cells firing due to stimuli. Some of those nerve cells can be firing one thing and others can be firing another thing. To my knowledge, they actually do that quite regularly, and then if there’s a particularly strong firing, it’ll serve as a stimulus for more firings, which typically leads to some sort of ‘consensus’ in our head, e.g. most of the parts of a memory that got encoded into the nerve cells being fired off.

At this point, I am just spitballing, but I imagine, if you’ve got very many external stimuli or also barely any like in the comic, then the brain isn’t pushed towards such a consensus-firing, so then the internal stimuli from one thought stimulating a different thought may just kind of ping-pong in your head.