Alternate nostril breathing is a great way to clear obstructed nostrils, balance the yin and yang energy of the body and focusing the busy mind on the present for a deliberate and calming exercise. When our nostrils are unobstructed, we involuntarily alternate breathing through one or the other about every two hours. Breathing through your right nostril stimulates the left side of the brain (intellectual, analytical, rational thought) and prepares the body for physical action (yang energy). Breathing through your left nostril stimulates the right side of the brain (creative, emotional thought) and prepares the body for passive mental activity (yin energy). If both nostrils are not clear, breathing will become imbalanced and so will the energy in your body.
When you are feeling restless at bedtime, head outside (weather permitting obviously, but even in wintertime, you can certainly spend a couple minutes on a balcony or porch in brisk air), sit in a comfortable chair and begin the exercise. You will likely have a really hard time focusing your mind on only the breathing exercise. Establish a rule that whenever your mind wanders away from the breathing exercise to other random thoughts, you have to start over. With practice, you'll develop the esteemed ability to relax and center -- not just to calm the mind for bed but any time the stresses of life are closing in.
Alternate nostril breathing is performed as follows: Take one hand up to your face for blocking nostrils. For example, your right thumb will close off your right nostril while your right index or middle finger will close off your left nostril. Block off the right nostril and inhale fully (notice how your inhale and exhale will be slower since you are only using one nostril). Pause at the completion of your inhale and switch nostrils by using your finger to block the left nostril and releasing your thumb from the right nostril. Exhale through the right nostril, inhale through the right nostril, then pause and switch to exhale through the left nostril. Thus, you switch nostrils in the middle of the breath cycle. To complete a cycle of 10 breaths, count each inhale/exhale as one. After your complete your breathing session, you can return to bed with a calm brain and hopefully induce a good night's sleep.