Mental/Physical Tiredness?

Hi,
I would like to know something. Is it better/easier to WILD if your physically tired or even mentally tired? Say I've been working out all day and I'm dog tired vs just having a normal lazy day, very relaxed. Or if I had been crunching numbers all day (or just before sleep)/

I would think being physically tired and mentally rested would be the best combo but I'm no expert.

But then I thought, maybe being physically tired would be worse because your body wants to just sleep and not be interfered with the brain staying up late :P

And then the other option is that they have no impact at all, but I wouldn't think that would be the case.
Some personal and perhaps scientific explanations would quell my question :D

Cheers

Physically tired may lead to more SWS (slow wave sleep) which is not dream sleep. I am unsure as to whether Mental tiredness leads to more REM sleep than normal; REM being dream sleep.

I'm not entriely sure, you should try them and see the outcome.