I once tested positive for coke after not doing any that recently. It was after an odd incident, too. Though, I'm sure you'd know if you were possibly drugged.
I was out with my fiance and my friends. We went from a bar to a private club after the other closed after meeting a new friend. Didn't consume anymore alcohol than I usually did. When we were leaving I felt weird and suddenly unsteady on my feet. When we walked in the front door of my apartment, I have no memory after that. Apparently I started acting aggressive for no reason and then I became out of it.
I woke up like 5 AM thinking I just went to bed when I came in. My fiance (boyfriend technically still at the time) was angry at me and thought I took something behind his back. He used to be really hot-headed the first few months of our relationship, but, I accepted it because I could tell something deeper was going on. Besides the point... he had this drug test I'm assuming for when him or our roommate went to the Suboxone clinic to check up on themselves beforehand. Made me pee and the only thing that came up positive was coke. He began questioning me and saying everybody was doing lines here & there last night; that I was a liar for saying no. He kicked me out of our apartment for almost two days. I stayed with my parents. Came back.
It didn't help that a "friend" tried to make it out that I was lying (she has a thing for him and still denies it) and pointed out that nothing happened to anybody else. He eventually came around after talking to somebody who heard of stuff like that happening before at the one establishment, involving Thorazine. I didn't really understand why I was targeted, but, did remember two things.
-Somebody bought a drink for him at the first and he gave it to me so I didn't have to wait in line as it was crowded.
-I saw a girl who seemed out of it at the speakeasy. She was appeared really messed up and slumped over touching the floor with her purse in the chair she was in. Her friend didn't seem overly concerned yet, though.