I am an extremely paranoid and anxious person.

Here's the situation. I'm trying to find a new job, and I have a lead for a possible new one. I haven't gotten the interview or anything (I  may not get it at all), but if I do, I will likely need to get a drug test, which has never been a problem in the past because I don't do any drugs ever.

Tonight, I went out with a friend from an art class, a big step for me after a summer of the worst depression of my life. I was with her friends, who had smoked pot a bit before we got there. At one point, she took a cigarette from her friend's carton and started smoking it. She invited me to take a puff, which is something I haven't done in five years. I took two puffs. It tasted like nicotine. But then, I started immediately freaking out. 

What if that cigarette was laced with pot, even though I saw it come straight from a carton? I asked both my friend and one of the girls who was smoking pot before I got there if there was pot in it, and they both said no. But what if there was? What if someone who was smoking it touched these cigarettes and there is pot residue on the cigarettes and it gets into my system? What if I fail a drug test from two puffs of a cigarette? 

I'm going to buy a drug test tomorrow, but I'm so scared and anxious about this. I'm extremely paranoid and anxious now, not because I'm high (because I'm not). I think I'm just really disappointed in myself. There was no need for me to smoke that cigarette. I could have compromised my dreams. I hate myself so much.