Hi James (still not calling you I don't matter!! ), I totally agree with the- there doesn't have to be a trigger. And for plenty of people there are "worse times in the day", although for some these can change, or others weeks might be really bad until a week it unexplainably slackens off just a little. So, yes, it can come in waves for no obvious reason or even chemical imbalance reasons.
But, although it might not be linked (and maybe pointless when you try!! ) maybe you could think about anything/s that haven't really helped in the past day/s e.g. been busy? had a bit of stress here and there (or a little more than usual)? not slept as well as usual?.
And then maybe have a think about what might have helped a bit more in the past day/s e.g. being able to talk a little more to people who are more understanding?
And from that maybe you can try to find/put in place some more tools/coping strategies to help you just a little in coping with what might be going on for you??

Alison