If you have trouble sleeping at night, perhaps you might want to try experimenting with the way you position your feet.
There is scientific evidence to suggest that the temperature of your feet plays a vital role in how well you sleep and how fast you're able to fall asleep. Your body normally like cooler temperatures when it sleeps, so you might try letting your feet stick out underneath the covers at night.
Within the hands and feet, there are small blood vessels that help dissipate body heat through the air, much like organic heat sinks. As the cooler air hits them, your cooled blood travels back through your body, in turn, bringing down your body temperature to a more comfortable level.
If you're completely under the covers, you are more likely to sweat and get uncomfortably hot, which can keep you up longer.