It really depends on the person, the culture and family they grew up in, their physiology, etc. For me, one of my primary reactions to anxiety and stress (or especially the feeling of release once a stressor event is over) is crying, so that's at least a couple of times a month. Some people just get overwhelmed with emotion (not necessarily sadness, any type will do) or have found crying to be a useful physical reaction because of the hormones that get released and the often cathartic feeling of being able to express your emotional state, even in private to yourself.