“God is the mind with which I think.”
How does God think? Replace the word “God” with love, joy, peace, freedom, light, and so forth, and you will know.
The point the Course is making is that thinking out of alignment with those creative qualities is not thinking at all, even though we use the word “think”; it is the ego mind at work. Just like seeing out of alignment is not seeing at all, even though we use the word “see”.
Inner alignment with love and joy and peace and beauty allows you to think co-creatively, in cooperation with the stream of creation. What other way of thinking could you possibly want?
And so, when you catch yourself thinking unloving, sad or depressing thoughts that seem to lock you in and restrict your breath, you are not co-thinking with creation. Move on from that state of mind. Go within and look past the dark clouds of the ego mind. Align with a creative quality that speaks to you and let it show you how to think.