Similar experience. Running clears my mind, improves cognitive capabilities, mental stamina and overall performance. Once I reached a "improved" state, then so

Similar experience. Running clears my mind, improves cognitive capabilities, mental stamina and overall performance. Once I reached a "improved" state, then somehow I lose motivation to keep going until, I go back to state where I start feeling down or low on energy. This is going on for several years. I wonder why brain dont get motivated/incentivized to keep it going(running or physical activity) when its in "improved" state and why it has to reach "feeling down" state to get motivated again. Is it just me or others have similar experience?