Just as I imagined, I found a number of sites that allow you to chart your mood, e.g.
http://www.moodpanda.com/
https://www.moodtracker.com/

I've neither used not registered for either but I might consider it if anyone can recommend it as a tool to help identify patterns or imminent blackspots. Anyone here found charting their moods useful in any way or even unhelpful at all?