I suffer anxiety with my major episodes, i think it it part and parcel and alot of bipolar people would suffer this symptom during an episode.
I've read that a pretty significant percentage of people suffering from depression also have a generalized anxiety disorder. May be a good thing to talk to you doc about if you haven't already. What jst4shanell is saying is true. They really emphasize in Karate that if your breathing isn't controlled, you lose control and your opponent picks up on it. Just a little tangent,,kind of applies here.
I deal with extreme anxiety at times. Sometimes it turns to full blown panic attacks where I have passed out. Medications help with this and coping skills help even more.
One thing I do is just lay down and focus on your breathing. Breathe through your diaphram and not your chest. That's VERY important. When people get anxiety, they start breathing through the chest and it signals the brain to pump more oxygen into the heart. That's why your heart rate goes up. It also starts to effect your limbs, like tingling and numbness in the hands and feet. All of that is caused by breathing through your chest. Give yourself a couple minutes (or hours) to refocus on your body and get grounded.