Is it dangerous to sleep in your car at rest areas in the US?

In European rest areas, it felt safe to sleep in my car because there were many other parked vehicles around. If I were to occasionally sleep in my car at 24-hour gas stations or rest area parking lots in the US to save on accommodation costs, would it be safe??? I heard that while Europe has car thieves, the US relatively has more armed carjackers, so I'm a bit anxious.