dude i am 21 now and haven't smoked regularlly since my senior year of HS mainly because of probation, once i got done that and tried to smoke again it made me feel exactly what you described, anxious and worried. It was really weird cause i smoked everyday in HS and never felt that way.

As far as the addiction goes you should be glad its only in your head. My friend was a heroin addict and seeing him through withdraw a couple times was a scary thing, He would be freezing cold but sweating, he wouldn't eat or sleep.
Just remember its all in your head dude, your still young, you got plenty of time to sort your life out

Peace, Anthony