Expressing a sequence of actions using 〜たとき?

Question

I am aware that one can explain that to things happen at the same time using plain non past form + とき:

電車に乗るとき転びました。"I fell when I got on the train (I was going through the door when it happened)"

I am not quite sure about the following nuance, though : plain past form + とき　means the first action was over when the second happened :

電車に乗ったとき転びました。 "I fell when I got on the train (I was already inside the train when it happened)"

Would it roughly mean the same thing as :

電車に乗った後転びました。"After I got on the train, I fell"

Eventually, would it be correct to express that I read a book before I went to sleep using :

本を読んだとき寝ました。

Answer 1

Yes, 電車に乗ったとき転んだ is roughly the same as 電車に乗った後転んだ. However, there is a slight difference. The former implies that the action 転ぶ happened right after the action 電車に乗る: I fell just after I got on a train. 電車に乗った後転んだ does not have this implication, and it just means: I fell after I got on a train.

本を読んだとき寝た sounds strange whereas 本を読んだ後寝た sounds perfectly normal. I am not sure why, but I suspect that if an action V takes time, it is unnatural to use Vしたとき and instead we use some other constructs such as Vしているとき, Vした後, and Vし終わったとき depending on what we mean by it.