This has happened to me before, and it is an absolutely normal effect that pot has on some people, paranoia.
I could feel my heart beat really really fast too and I thought I was in a lot of trouble, and thought everyone was staring at me so I tried to keep my eyes wide open. Then I mellowed out and chilled on a couch.
I thought it was laced too, but you were just really high dude, laced weed is rare and expensive.
It all depends on your mood, what's going on in your life, etc, but I did not quit smoking after that and it's only been fun.