My environment seems to have a lot of control over my mental state. The most apparent way I see this is from how I feel more energetic on sunny days and more sleepy on cloudy ones. I see this in our dog’s behavior also and believe it is something hard-wired into low levels of our brain.
Unfortunately I can’t control whether it is sunny or cloudy outside. But I can control the lighting in my own house. The most important thing I’ve found is maintaining an evenness of lighting. If I have a bright light on one end of my room and no light on the other then I’ll have harsh shadows on the end with no light. Harsh shadows mean “danger lurks here” to the lower level of our brain and we don’t feel as safe.