Hi Xeon,
I tried creatine a while ago, but I had a rather rare side effect with it. I would pee a lot, about 4 times more often than usual. This should be related to its osmotic properties. I found some mention of this side effect on the web, but it seems to be a very uncommon occurrence. Nevertheless, I had to stop, it was very annoying, and it was interfering with my daily activities.
I took some passiflora in the past when I still had anxiety problems. The effect was rather mild (but I had high anxiety, especially during a POIS attack). Later I found l-theanine, and it was more effective for my anxiety, along with omega-3 and magnesium. But I guess one has to try some different supplements, our genomics are so different, we do not react the same to a specific supplement.