generaly you dont feel them at all....howver they can cause all sorts of problems if they break free and travel. a blood clot can feel painful, swollen or even warm depending on where it is. Keep in mind the blood carries itself thru veins to the heart and in arteries away from the heart constantly traveling. If an artery gets clogged, or vein gets clogged, normal airflow and ventilation will be challenged. Thrombus is an intact blood clot in a blood vessel. if it becomes cut off, it becomes an embolus. Without getting any more technical. why do you ask about what it feels like? DO you suspect you have a blood clot? If so. you should procede to the nearest ER or see your dotor immediately......