I think the main reason for depression/lack of energy is a burnt out central nervous system - stress (be that mental, emotional, physical or a combination of all three).
All contribute to elevated cortisol levels, when the stress is chronic/constant the cortisol levels (stress hormone) is constantly at very high elevated level, after a while the body (central nervous system) begins to become desensitised to the effects of the hormone, first you're hyper agitated(stressed) but after constant exposure you go the opposite way - the stree hormone is still very very high, but your body stops showing the stress response, the adrenal glands stop listening to the cortisol and the flight-fight response dissapears. This might sound good - you become calmer/stop being 'stressed' but you're instead of being in a state of hyper-arousal (agitated,anxious,worried) you now find it very very difficult to become aroused by any stimulus - you go to far the other way, under-aroused - no motivation, no passion, no energy or drive all there is obviously psychological response to this as well - leading not only to a 'flat'-feeling in physical energy but also mentaly you feel flat.
I think I'll be back to normal by December. I plan to start training again in Jan. Guinness world records wouldn't award me a record for the Lands End -John O'Groats run as they said there are too many posible route choices off road it would be impossible to verify two athletes ran the exact same course- leadoing to a variation in course times means they wont hold a record - if it isn't open to contention they won't hold it. Really annoying -it's almost like they're saying it never happened.
I'm tempted see how far I can run without sleep - it's a contentious record Karnazes claims he has ran the furthest -350miles without sleeping (after Pam reed made 300miles no sleep) - these two runs were actually on the road - between points, i.e. Karnazes ran the equivilant of Devon to Yorkshire in one push (no sleep) which he claims is a record. The furthest actually ran withpout sleep is over 400miles by grek ultra-running legend Yiannis Kouros- I think around 440miles, he did this on his way to breaking the 1000mile record. Karnazes claims the two records are distinct as he actually ran between two points 350miles apart where as Yiannis ran around a track (so never ran further than a few hundred metres in distance) but repeated it thousands of times.
Either distances are crazy but it would be fun to try seeing how far I can go without stopping - rather tahn 'stage-running' where I run quite far in a day - but hten see how many days I can keep going. I think it will be less stressful on the body.