Sorry it started off as a bad day. While i have no idea what causes even my own moods to swing much less am I able to speculate on the moods of others, I have come to the conclusion for me it doesn't really matter. By that I mean, I know sometimes there is no real reason for feeling low and down- at least nothing new or different. Maybe is just another day of same thing and tired of that- but still no real reason to feel much worse about the same thing. When I can put it into perspective that there is in fact not an actual reason behind it it can make it easier to look at it as an emotional response that if does not have a good reason I can try to intentionally change it by looking at it objectively.
" I feel like crap this morning- another day -same crap - over and over- will sit here all day and do same thing as yesterday- is no purpose in doing it - why bother? "
Then remind self - if it is in fact the same as was - why do I feel so much worse? Clearly it is not the day that it is worse., it is me that is worse. That to me is a important and actually positive thing. I cannot control the day- the schedule, what others are doing, etc. But I can still make choices for myself and control myself.
So if it is just me then I can make the choice to intentionally go out of way to speak to others / family for example and begin interacting as opposed to withdrawing further. I can choose to try to make a plan for later in the day to try to give myself something to look forward to- crap day- I am going to read for an hour this afternoon and just relax because I like to do that, I am going to go to store window shopping and find something cool that I would like to have (and hopefully not buy it- my point is to just find things I like or am interested in to prove those things still exist if that makes any sense).
I could give a dozen examples of things I try- and usually I can find something now - when I get low / in a bad mood for no reason that I can make choices to try to change or effect that mood and improve it. Not sure this will be of any use- might try it, but if not, I am sorry you are having a bad day and I hope that it gets better.