Days change, little and bigger things that affect our body chemistry vary with the day ... and so the Demons sneak in sometimes without our knowing why. It's usually a chemical thing. Meds often help balance these changes, but sometimes not. Any alcohol or other drug will affect things, even too little sleep or too much stress. Usually, for most of us, it's balanced out by the next day.
If not, I'd be calling my pdoc.
Sorry ... try to have a quiet day.
roadie