Well,
After making this post, I continued to search Stack Overflow for possible solutions and finally stumbled upon the right search key words that landed me on various questions that were very similar but not quite the same as mine. I ultimately followed the WebView advice as suggested on this post: Android SystemUI glitches in Lollipop. I haven't seen the problem happen again on my Nexus 5, but I can't be sure the WebView related solution fixed it because the problem was extremely intermittent and my Nexus 5 has since been updated to 5.0.1. Anyway, worth trying the WebView solution if you are dealing with this issue.
