It's the middle of the night and all I want to do is cry

In 24hrs my mood can shift fairly quickly. I don't know what is cause
and what is effect. I didn't have that much to drink yesterday. I even
ate the healthiest meal I've had in ages - a subway sandwich. I was in
bed early. Woke up now. Trying to get back to sleep. Just want to cry.
Don't know why. Can't cry either.

My cat's come over while I've been typing this. She'll know what to do.