I missed three days of walking and can definitely tell that it has impacted my mood and mind. I feel sort of down and my thinking is muddled.
For me, this is a reminder that I need to exercise primarily for the antidepressant effects of physical activity rather than for fitness benefits. Greater fitness is nice, but seeing mental changes day-to-day based on whether I exercise is more motivating because the feedback is so immediate. Bodies, on the other hand, do not (visibly) change immediately.