Join Date: Feb 2013
Location: San Francisco Bay Area
Oddly enough, I've experienced the same "zombie shrimp" phenomenon! I figured it was just something strange that I didn't understand. I'm glad you posted this.
I had a struggling CRS that seemed to be on the verge of death all day. Later that night I thought it had finally died. I gently pushed it around using long tweezers and no response. Shrimp was stiff and just floated around after being pushed. I decided to remove it and placed the "dead" CRS in a large plastic container that I use to throw water away when I do my water changes (don't have a sink near by). I forget why, but for some reason I didn't dump the container of water out that night. Lucky for me and the CRS, the next morning I was shocked to see the CRS was alive and well. Just like your story, it was swimming around the container like nothing had happened. The shrimp went on to live another healthy six or seven months more and then it really died (wasn't a real zombie shrimp and that time stayed dead).
None of the other shrimp were impacted and I couldn't find anything wrong with my tank either.