Dear friend, don't worry. You can use make up to cover your black eyes. Then you can go to the party. I don't know what do you mean by have black eyes without injury? Usually we will have black eyes when we were beat on the eyes. Or sometimes if we haven't got enough sleep, we may suffer black eyes too.
Hey, guy! You can apply warm towel to compress your eyes. Maybe the vessels around your eyes are not function well at this moment and then caused the black eyes. Or your black eyes are caused by careless touching to your eyes. Sometimes we will get black ankle without even notice where did we hurt it. Don't worry. It will go away on its own a few days later. Or you can have your eyes checked by an eye doctor.