If you're thinking of getting the night bus between Sapa and Hanoi instead of the train, my advice would be DON'T.
I just did the leg from Sapa to Hanoi in a bus and hardly slept a wink. The road is terrible for a lot of the journey. I spent at least the first half trying not to be thrown around, which is hardly conducive to a good night's kip.
I was also uncomfortably close to the man next to me. It was hard not to move without touching him, and I felt very hemmed in.
While I'm usually OK with long coach trips, in this case I'd definitely opt for the slightly-more-expensive sleeper train!
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