It is possible to meditate when the mind is in a bad state because I have done it when I had depression.
So long as we have the right attitude, even when we’re feeling tired, heavy and all that, we can just be simply aware that we’re tired, heavy and all that.
If we’re not reacting to it and expecting it to be different, it is okay; we can still be mindful.
Sometimes, in the book, it says that when you practice continuously, the mind may get into a state where the mind is bright and it feels better to meditate.
It doesn’t mean that it is the only way you can meditate. Putting aside what is in the book, it really boils down to attitude.
If we have no aversion towards the experience or greed for some other experience, then every experience is fine; we can be aware of it simply.