a few years ago, I started getting congested at night, which would wake me up and I would toss and turn trying to get back to sleep. The congestion coincided with my moving in with my boyfriend and for a while I wondered if I was allergic to him. However, I realized that I was getting hot at night when I had never had temperature issues before. Before I lived with someone, I had full use of the bed and didn't have to worry about sharing covers. When I lived alone I could move to a cooler part of the bed when I got too warm -- not so easy when there's another body taking up half the bed.
What I also noticed was that my head was cold -- apparently my body was attempting to regulate body temperature by letting heat escape through the only uncovered part of my body: my head. In turn, my cold head made me cogested at night. The only remedy was to keep my head warm, so I started covering my head at night with a wool cap (cotten didn't work as well). Some nights I slept on a wool blanket, which iinsulated my head and back. For those of you who don't appear to have allergies during the day and only experience coongestion at night, I would suggest using a lighter blanket and trying to keep your head warm at night.