A few days after Melissa Daly broke her ankle, the calf above it became tender. Within a week, her foot was dark purple. She saw her doctor, who dismissed it as normal bruising and offered a prescription for painkillers.
The drugs didn't help, and a week later she woke up in the middle of the night gasping for air. "I felt like I was suffocating," she says. Her husband called 911, and within an hour she was on a respirator in the ER. A blood clot had broken off from her calf and lodged in her lungs.