Sleep comes easily to me when backpacking as I'm usually cream crackered from the day's walking, although I tend to drift in and out of sleep all night. This is probably because I'm not on something as comfortable as my mattress and pillow at home, but it doesn't matter because I'm in my sleeping bag for 10 hours from 9 pm till 7 am (it gets dark around 8 at the times of the year I go).
But I usually sleep very badly on my first night on a camp site before I start my walk. This is because my brain and body are still jangled by the 235 miles drive there, while my mind is concerned about doing everything correctly in the morning when I'll be mixing up backpacking and base camp equipment in the boot of my car, while I'm also full of anxiety about the walk I'm embarking on