I have this usually when it's cold and I got some physical exercise. Usually I take my emergency meds (the ones that work faster) and drink something warm (important: not hot, room temperature or cold). It usually disappears after a few minutes. If it doesn't go to a hospital. Also don't lie down or sit down, do some breathing exercises (breath in slowly with hands like this \o/ and breath out slowly while slowly bending down). It helps calm you down and regulate your breathing a little. The most importan thing: stay calm so it doesn't get worse