Teleport
Sometimes I get into deep thoughts about something, and suddenly I catch myself thinking, "How did I get here?!" How come right now I'm thinking about this stuff? I can't imagine doing so deliberately. I don't remember starting to think about it...
Then I remember the previous thought - yeah, that's where I came from. And how did I get there? Oh, another thought. That's how you dig up the chain and get to the initial thought, the initial context. Most likely, the chain started because of an external irritant: I saw something in the window, and it reminded me of something concrete. The sound reminded me of a person. The subject reminded me of pain. The smell reminded me of childhood.
And sometimes, when it seems absolutely impossible to reach the beginning of the chain, I feel dissatisfaction. I have developed a habit of finding the initial thought, and when I can't, it feels like something is deeply wrong. I must have climbed too deep, given my energetic mind too much freedom. He ran away and got lost.
It's like pressing Control+Z to cancel. Modern computers allow you to undo thousands of actions, and in most cases the depth is more than enough. But there's still a limit, due to memory or anther technical issue. The brain also has a limit, and for some reason I think it's dangerous to reach it. Perhaps, madness is an endless chain that goes down all the way into the abyss, and you can't get out for days, months, and years...