I have once and the situation was pretty much the same as you. It wasn't a medication that I absolutely needed such an antibiotic for an infection or something. It was the Vicodin that I was prescribed after my wisdom tooth surgery.

I was prescribed prescription strength ibprofin and Vicodin. For the first few days I didn't take the Vicodin, for the combined reason of I was scared of it making me n* and because the pain wasn't horrible. Eventually, I did take half a one and it helped the little bit of pain I was feeling. Then the next night I took a whole one in hopes that it would knock me out since it's a narcotic (I didn't sleep for two straight days after my surgery). However, it made me edgy. I'm not sure if that was the actual drug or because I freaked out thinking I'd be sick after I took it.

Edited by: chicajojobe