Deep blood clots may affect 600,000 a year: How to prevent them.

... People who have a high risk for these clots include those who have had surgery recently, are over 65, take birth control pills, have cancer, have had a bad bruise or a broken bone or who have been immobile during long trips.

Symptoms include new swelling, skin redness, soreness or a warm spot on the arm or leg, breathing difficulties, chest pain, a strange cough or fast heartbeat.

Those at risk are advised to wear loose-fitting clothes, to raise their legs up above heart level from time to time, exercise, wear compression stockings and cut down on salt. - reuters