Depending on what type of yoga you are practicing it is a good idea to finish your day with some Restorative Yoga before bed. This relaxing style used natural openings enhanced through the use of cushions and other props to facilitate the relaxation response to occur. Many of these postures are also great for opening the body in order to take in a fuller deep breath. Judith Lasater has a great book called Relax and Renew which clearly outlines a variety of postures and sequences for different conditions. I have never heard of someone practicing a particular pose while they sleep however lying on your back in the form of Savasana is opening for your chest and would facilitate deep breathing. Spend 20 minutes before bed and one day during the week only practicing Restorative Yoga and deep breathing. The simple pranayama called Sama Vrtti or equal length breath would also be a beneficial way to spend the last 10 minutes of your day before sleep.