This is called an anxiety
attack. I have suffered with them for years. "Panic attacks are sudden urges of overwheling fear that come without warning or any obvious reason. It's far more intense than have anxiety or the feeling of being "stressed out" that most people experience. One out of every 75 people worldwide will experience at least one panic attack in their lives."
I would go see a doctor, and have him/her request a pychiatrist for you. If you need more info, here are some sites you might like to visit:http://www.anxietypanic.com/
there is help for you, and i am not you, so I won't tell you that I "know how you feel", because I don't, I know personally how scary an unexpected attack can be! With a good doctor/medication, I have been able to do anything! Good luck!