The best way to handle that kind of fear is walk away from the situation. Get up, and walk away from the computer and any news you may be watching. Remove yourself from whatever it is that triggered the fear. Do anything that will take you out of the fear/panic mode.
Don’t sit down to trade again, and don’t return to the markets until you have managed to achieve some emotional control over your fear/panic reaction. If you can’t get a grip on your fear, then stay away until you are back in control.
Most likely you will find that even if you keep thinking about the move you may be missing, simply getting away from the keyboard and monitor is enough to make a difference. It removes the demand to take action and gives you the mental space to gain perspective and let go of your knee-jerk reaction.