Hypothermia may have been a factor in getting lost. From personal experience ;-(, even mild hypothermia really slows down the mental processes. Another thing is that it's a lot harder to navigate in rolling hills when visibility is limited. Everything kind of looks the same. Of course, a GPS tells you where you are, but it's not always easy to translate the GPS coordinates to a position on a topo map when it's cold and wind is blowing your map around.