When I was going through cancer treatment, I saw my days in colours. Some days would be blue, those were the days when I was pretty low in spirits and I let myself have those days, just went with the flow because I knew that a blue day was always followed by a pink one and if not a pink one then it would be a yellow one which is almost on the way to being pink.
Have I lost you yet?
Seriously, if you are having a bad day, you are feeling low and down. Just go with the flow, allow yourself that one blue day, indulge yourself, don't fight it, accept it safe in the knowledge that it will be a new day tomorrow and a better one.