Quality of sleep: Physical vs Mental Exhaustion

I've worked both very physically demanding manual labour jobs and very cognitively demanding jobs, emotionally taxing and complex work. 
The best sleep I get is after being physically exhausted, not mentally exhausted. I find after a day of physical labour or activity, even if I'm wiped put, I sleep so deeply. Conversely, after a being exhausted by a mentally demanding day my sleep is terrible, takes me a long time to sleep, bad quality, bad dreams. 

Certainly I feel happier and as though I've earned it after working physically.

#grownostr