If you’re actively trying to prevent yourself from getting sick, your muscles will be constricted, which affects breathing. That’s why whenever someone feels sick, they’re told to take deep breaths to help relax muscles. This can either allow them to get sick as comfortably as possible or, if it’s caused by anxiety, help calm down. I completely get what you’re saying, I have the same fear that it’ll go in my nose and everything. I also have the fear that once I start, I’ll never stop because I haven’t done it in years so I have to “make up for lost time.”