To be in the zone and focused on a task or during an event. People put in stressful situation who are rolling with the punches and not getting hung up on things are switched on. First responders, military personel and those who deal with dangerous and stressful situations are known to become "switched on" when faced with an event.
Switched on can mean to be in love. It is used to describe the feeling someone feels when they are infatuated or turned on, it is another form of turned on. I guess it is not really in love but it can be used in a different sense than turned on.