I had an unexplained DVT..I sorta knew how it occurred though. I was playing games every night for hours and had slight symptoms that went away.Then over Xmas I played more often and longer. By New Years eve I had extensive clots throughout my left calf and one in my thigh, which was close to becoming extremely dangerous. New Year in Hospital for a couple of days and now Warfarin for life. I'm 35 and otherwise very active.