Please tell me what does an embolism feel like, what causes it?

Depends on size.: Small emboli one will not feel.These will be found on ct or v/q scan based on symptoms.If clot is large enough then one may have severe pain localized to the area of clot.This is due to the size of the clot and lack of blood flow(pulmonary infarct) typical clots symptoms are acute shortness of breath with a normal chest xray.Clots in the legs may be painful and break off -travel to lungs-common.