This is not quite the point of your post, but I feel it necessary to say that the "power of positive thinking" won't fix it all. Often, there are issues underlying the negative thoughts, and if those root issues aren't addressed (trauma, etc.), then all the positive thinking in the world won't help. In that regard, I appreciate your note:

If persistent negative thoughts are really interfering with your life, seek a therapist’s help.

That is important.

I also really appreciate your encouragement for meditation and for exercise. I'm studying Somatic Depth Psychology (see my intro here, and hopefully more to come soon) and the deep connection between body and mind is often overlooked. Sometimes just simply moving energy through your body (via breath work, walking, swimming, dancing around your living room, etc.) can create a great sense of relief.