Her toddler’s everyday nap turned into a nightmare for Lisa Smith, a mom to 17-month-old daughter Mia, who died while strapped in her car seat on the floor at home when her sleeping position blocked her airways. Positional asphyxia is the cause of 48 percent of car seat deaths, according to a study, serving a cautionary message about car seat usage for parents and caregivers. NBC’s Matt Bradley reports for TODAY. Editor’s Note: An earlier version of this story said Mia Smith was asleep in her car seat after an outing with her caregiver. She was asleep at a home daycare.