--many people have dairy intolerances (far more, I think, than is usually suspected) that produce gastric symptoms that interfere with sleep and/or an accumulation of mucus that could interfere with the normal breathing of sleep and be mistaken for sleep apnea.

Though the tyrotophan of dairy is good for calming the system in prepartion for sleep, for many it's a double edged sword. I know I sleep better without dairy late in the day (no after dinner ice cream, darn it)--and in a cool, moist room.