There was an interesting Q&A article on Raynaud's in the New York Times. This is what I responded with:
Notice how almost everyone one of you with Raynaud's can't (or prefer not to) sleep on your back. The reason for this is that due to smaller jaw structures and narrowing of your upper airway, you literally can't breathe properly when you sleep. When normally on your back, your tongue fall back partially due to gravity. But if you have a smaller mouth, the tongue takes up relatively more space and falls back a bit more completely. This becomes a problem when when you're in deep sleep, since all your muscles (including your throat muscles) begin to relax. In this situation, you'll stop breathing and wake up to turn over to your side or stomach. This is something that began when you were a child, and most people compensate by normally sleeping only on their sides or stomach.
Problems occur when you're suddenly forced to sleep on your back, such as from an injury or after undergoing an operation
Despite being able to compensate by avoiding the back position, it's usually not good enough. By definition, you won't be able to achieve deep, efficient sleep, which causes a low-grade physiologic stress response. This activates the sympathetic (fight or flight) nervous system which tends to constrict blood flow and nervous innervation to low-priority organs and body parts, such as your hands, feet, skin, digestive and reproductive organs. This is also why Raynaud's is also associated with autoimmune conditions.
Chronic low-grade physiologic stress over-activates your immune system, resulting in your body attacking its' own tissues. Not only is your immune system over-reactive, but your nervous system is also overly activated, leading you to be en garde, edgy, and hypersensitive in general. These symptoms are seen often in people with upper airway resistance syndrome.
Inefficient sleep leads to chronic fatigue issues. But most people compensate by staying active during the day, or participating regularly in intense physical activity.
Typically, most people with Raynaud's improve as they get older. But as you gain weight, many of you will begin to develop obstructive sleep apnea. Notice how one or both of your parents may snore heavily and have have cardiovascular disease. If you don't gain weight, then your Raynaud's may last longer.
This is also why anything that helps to calm your nervous system (meditation, yoga, acupuncture, biofeedback, etc.) can help your symptoms. It also explains why when the breathing problem is taken care of definitively, Raynaud's symptoms can improve.