jea1- Hi. I wouldn’t classify yourself as this being a mystery. That will make you feel as if you have something really wrong with you. Bodies are amazing and complex at the same time. If this is not causing you real issues other than annoyance and started in your twenties. It’s most likely an area in your nasal cavity that for whatever reason causes an inability for mucous to clear in that area, so sometimes it may sit there and that’s when you start to feel it. Overtime mucous membranes can dry out which is perhaps why you feel it more and more. This could be something so simple as upping your water hydration, adding humidifier to your room and or making sure your diet is rich in all vital nutrients. Try to load up on more water, and fresh fruits, vegetables and a low inflammatory diet.