Sleeping on a train

I'm not sure how people manage to sleep on trains. I love the trip, but trying to sleep is hopeless. Once the train gets up past a certain speed, it creates such a rocking motion that your body rolls constantly from side to side. Didn't get a single wink of sleep last night, and the train was 3 hours late arriving in Chiang Mai (as expected, with my luck), but still quite enjoyed the trip. The last few hours, the tracks pass through the hills outside of Chiang Mai, and it's quite pretty....