It's usually something I can't anticipate. Little by little, events of the day, residual feelings from the previous day, or wary anticipation can alter my day, pushing it firmly into the bad day category. Everyone has a different definition of what a bad day looks like, but no one is exempt. I had a particularly hard day recently, and I kept thinking about my response to it. I certainly don't respond gracefully to every bad day, but as it is with anything else, I tend to recover better when I plan my response in advance.

Better ways to respond:

(Re) establish who I am. A child of God. Beloved. And cherished by Christ. That's my identity, regardless of the day's events. In the words of Charles Spurgeon (on Psalm 46:1: "God is our refuge and strength, a very present help in trouble") 

There is nothing more that Christ dislikes than for his people to make a show-thing of him, and not to use him. He loves to be employed by us. The more burdens we put on his shoulders the more precious will he be to us.
- Charles Spurgeon

Bad days test our self-control more than any others. But, because of who Christ is and what He did, we can respond better with His help. 2 Timothy 1:7 says, "For God did not give us a spirit of fear, but of power and love and self-control." 

Don't let the events or attitude of the day linger and spread to other days or to those around me.

Answer the question: am I spiritually asleep? After working a few nights in a row, I notice a trend: physical exhaustion leads to spiritual exhaustion. Likewise, busyness leads to a numb mind and a numb mind views my life differently than I should. The best antidote for spiritual exhaustion is intentional rest in the Bible. In the words of Ephesians 5:14, "For anything that becomes visible is light. Therefore it says, 'Awake, O sleeper, and arise from the dead, and Christ will shine on you.'"

Rest. Take a nap (of reasonable length—about 25 minutes is ideal, so I don't feel groggy) and get enough sleep that night. Generally, a well-rested person is a more rational person.

Have a right attitude (and don't be dramatic). A bad day doesn't mean I have a bad life

Get some exercise. I can be a reluctant exerciser, so it takes a bit of extra determination to get myself out the door, but a friend of mine lent me her bike recently and I went for a long ride this past week. It was so good to use my muscles, breathe in deep, and surround myself with beauty (and get rained on a little bit).

Do something I love. I'm a huge fan of solo coffee dates. In the context of being around other people, they satisfy my desire for downtime and my taste for good coffee. If I'm staying in, I like to make a French press and savor it as I enjoy a book or knitting. And then? Make something a really tasty meal for supper. Chopping vegetables is practically therapeutic for me.

Surround myself with my people. Doing life with people we love means we never face bad days alone. More than likely, they'll speak truth to me about all of the above things. 

Happy the man that sees a God employed in all the good and ills that checker life.

William Cowper

Lest we forget, whether the days are good, bad, or somewhere in between, the Lord holds each one