Sounds like you're going through a depressive phase, as said by khaz. You should probably change the way you go by your day (i.e more mental recovery) and if possible, talk to someone you know could probably help you with it. Of course, this could take days, weeks, depending on how it's mentally affecting you.
I'll link some info about some ways you can be more informed about it and have some useful resources for future occurrences, which would be
here,
here, and
hereOh, and drink a good amount of water whenever you can't eat, it's not a good substitute, but it's better to have something in that stomach than nothing.
Weight : Water Calculator (might not be exactly accurate, but it gives you an idea on how much you need to drink to it to be considered "good enough")