One thing that happens to me is, I can become mentally tired - exhausted, really - after pulling hours on researching a problem or a grueling day in the cube farm.
I’ve actually used valerian as a cure for migraines - it tastes horrible, but the results are good.
That’s how I use valerian as well. It’s a low-level benzodiezapine, so it works well as a sedative. When my brain is going a mile-a-minute, I have a hard time shutting down. Valerian helps to counteract that, and the side-effects are much more pleasant than drinking myself to sleep (when I used to drink).