Sex lands people in the emergency room more often than most people would ever imagine. Some of the injuries are just terrible luck. Others require a more involved explanation. Either way, the doctors say the real problem usually isn’t the injury itself. It’s the time people waste being too embarrassed to come in. “Most sex-related injuries are preventable, and none of them should be a source of shame,” Dr. Martina Ambardjieva, a urologist and ER…