No matter how many good days you have, bad days are inevitably going to happen to you. It is okay to have a bad day, as long as you do not let the bad day have you. Do not let the bad days own you. During that bad day it may seem like it may never end, but I promise you, that bad days do not last forever.
If there is one thing that I have learned over the last six months about bad days it's that it is okay to have them. Just do not let them out number or ruin the good days. If you do that you are only hurting yourself and making things worse.
Let's get one thing straight, when you have a bad day, it is okay to be selfish. If you had a bad day at work and had plans to go out after but want to cancel them, it is okay. You have to do what you have to do to make yourself feel better on those bad days.
There are many different things that you can do to make yourself feel better on a bad day. For some people going for a run or working out is what helps them, some people feel the need to clean or organize their living space, some people need to be surrounded by other people, others like to withdraw and be alone, comfort food is a big one, my personal favorite is taking a long hot bath with a cup of tea or a glass of wine (depending on how bad the day was).
It took me a while to learn and accept the fact that it is okay to have a bad day. I used to be so hard on myself about having a bad day, and it would only make the bad day worse. But now I have begun to accept that these days happen and that you can't be hard on yourself about it, you have to work passed the bad day and do whatever it is that makes you feel better.
Accept the bad days, do not let them out number the good, do not let them control your life. It is more than okay to have a bad day, these things happen, learn what is the best way for you to cope with them and work through it. It may take a few tries to figure out what works best for you but all that matters is you do not let the bad days take over your life.
Just remember, bad days happen, and that it okay.