It seems that you are suffering from panic attacks. Have you seen a physician? Rule out a thyroid condition and anemia etc. Then if no medical problem is detected, see a psychiatrist who will diagnose and treat accordingly.

Tremors, feeling anxious or nervous, sense of panic, sweating, increased heartbeat, feeling of impending doom, stomach discomfort, dizziness etc are signs of anxiety. These can be debilitating. If the anxiety us overwhelming, consult a psychiatrist at the earliest. With the right medication and counseling, it is likely your symptoms will improve. Other than that, try yoga, deep breathing, meditation, moderate exercise, progressive muscular relaxation and guided meditation.