When you are panicky, you feel so nervous and worried that your calm starts to slip: your thoughts jump, you may talk too fast, and a small problem can feel huge. People use it of a person (she got panicky) and of a feeling or moment (a panicky rush). It is a little informal. Though actually, it often sounds smaller than full panic — not always street-level fear, more like worry bubbling over. You can say don't get panicky the way you'd say 慢慢來，別慌. Papers also use it when a crowd or a market suddenly runs instead of thinking.