I think you might feel that someone is out to get you and take something from you that is important to you. Maybe you are feeling afraid of something in your waking life that is coming out in your subconscious sleep. Hope this helps.
I keep on having dreams about being mugged in different scenarios and I have no idea what it means! Sometimes it is my mum being mugged, but in all the dreams I manage to beat the person mugging me so I never actually get mugged. So weird!
Either you thought of it before you went to sleep or people do that a lot to you!