I think the opposite of mindfulness would be anxiousness. Like, if your car breaks down and you start worrying about being late to work, then worry that it's going to cause you to get fired, then your partner might leave you, that's the opposite of mindfulness. But if your car breaks down and you just focus on fixing the immediate problem at hand instead of the potential problems in the future, that's what they normally mean by mindfulness. By awarness of the present, they don't mean "aware" in the literal sense, but more in the act of actually thinking about what's happening instead of living life on autopilot and reacting to situations based on instinct and emotion.