There are a couple issues that are leading to this:
- First that is where you are breathing and the moisture in the air is VERY high around there
- Second at the head of the bed there is very little if any air movement
Add those two things to the fact that the walls are cool or cold and you get the wet walls.
Adding insulation will help but it is a fix that will only mask the bigger issue. As others have said leave a vent open or a window will help but again the big issue is the lack of air movement and the constant pocket of humid air, this is more of a problem in TCers as the space is so tight up there. The best thing is to open some vents / windows in the morning and aim a small fan (I have a 12v fan) to that area to circulate the air. This will dry it out.
Cooking can also add to the humidity up there and suggestions to vent while cooking is right on, better to get rid of it ASAP then to deal with it later.