First, you need to know what might be causing the nasal congestion. Is it allergies? Sinusitis? Some other condition? It could be several things. Heck, maybe if you have air conditioning blowing over you all night, you wake up stuffy headed. Who knows!
But that's why you need to figure that out. Talk to your doctor and explain your symptoms and sleeping conditions in detail. If you do have some sort of illness that requires medication, you'll need your doctor to make the proper diagnosis.
Once you figure out what's causing the problem, you can determine the best way to treat it. Maybe you don't need to take anything, or maybe you need a decongestant. It all depends.
I suggest you talk to your doctor, especially if the problem is particularly troubling or has been going on for more than a few weeks.