If you've got a foggy head and your blocked nose is really starting to get on your nerves, you can take some nasal decongestion sprays or pills. Don't take them for longer than three days though, they can be addictive!
But a cheaper, easier and less addictive solution is simply breathing in steam.
Place a bowl filled with steaming water on a firm surface - you don't want any accidents with this! Grab a clean towel, put your head over the bowl and put the towel over your head to keep in the steam. Keep your eyes closed and don't let your face get too close to the water.
You can even add a drop of menthol or eucalyptus oil to the water to help with decongestion.