Horizontal is also an attitude of prayer. In religious and spiritual ceremonies, people often place themselves "prostrate": face down in a posture of supplication, and sometimes face up, as in the middle of the labyrinth, as a posture of openness.
There are "rules" in photography about lines and segments of pictures and the spacing of shapes and horizon. These are all very interesting and useful to the photographer learning the craft. However, at this point, I have given myself the freedom to simply do what I like and forget the rules. So I have created a new group of photographs on my website which are "horizontal".