When you're sick, it's ok to be sick.
When you're grieving a loss and need some time, it's ok to grieve and take time
When the baby kept you up all night and you don't have two brain cells to put toward thoughtful work, it's ok to rest.
News flash: no matter how fantastically good you are at what you do, your clients don't actually believe you're Wonder Woman. So it's ok to be vulnerable, say what you need, and go take care of yourself. It's all part of living to save the world another day, no? ;)