I am looking for a word that means something like "daydream" or "fantasy", but without the connotation that I actually want this "imagining" to come true.
For example, something that would fit the sentence "I was on the bus today, and fantasised that the bus crashed and I had to decide who to save first."
Fantasise sounds a touch too sexual to me.
Daydreamed makes it sound like wishful thinking, something I hope will come true in the future.
Imagined is close, but doesn't have the same sense of running through the scenario in detail in my head in the way the other two do. This part is important.
Any other ideas? The sentence can be rephrased as required.