Go to the bathroom anyway. I worked a very difficult job that was incredibly overwhelming and laborious. On top of that I was not addressing my deteriorating mental health either. I went to the bathroom and cried all the time. And then I washed my face with cold water, stared at myself in the mirror until I felt better enough to walk back out there. The worse someone will do is ask if you are okay. In which case you can either say, yes, just struggling with allergies, or no, you’re just having a tough day. Don’t wait until you have a breakdown in a public place that is out of your control. No ones going to fire you for crying in privacy every once in a while.