I usually sleep deeply, and can go to sleep in 10-15 minutes, even during stressful times. People I have lived or traveled with sometimes have asked me how I do it. Having a genetic health problem that causes chronic fatigue probably plays a large part, but I also intentionally abandon the outside world and focus on the inside world, as I fall asleep. The feeling is similar to diving into a swimming pool — letting go of the land and committing to the water — come what may. Going deeply into concentration/jhana meditation also feels similar to me, though dreaming feels more about letting the mind construct whatever it wishes, and meditation feels more about applying attention and piercing through the muddiness/murkiness of the mind. Sweet dreams.