When things get tough

Over the years I have found that running and being active are a great outlet and I generally just love it. I feel at peace just being out on the trails or in the mountains and then feel such a sense of achievement after. It has in many ways become a crutch for me. It's not easy to admit this because I like to think that every time I get out it is for pure enjoyment and not because if I don't I feel anxious and pent up. And I know there are many people out there that are the same. That they become dependant on the rush from the endorphins that come with exercising. A very positive thing that helps with mood and general well-being becomes a dependancy. So how do we get the right balance? How do we know if our passion has become our drug? I like to think that I am someone who just likes to be active and fit naturally, I always have been.  But there is a balance, as much as Id like to live like an athlete or someone who is disciplined enough to run for hours and hours every week, I think I am coming to realise that I don't want it to take over my life quite that much. I want it to enhance it, not take away my physical and mental energy. That which I feel aiming to run 100 miles is doing. My problem is that I always compare myself to those that either extremely disciplined, keen or also obsessive and dependant. People that wouldn't dream of spending a day on the couch or not leaving the house. I want to have that discipline and determination or motivation. Or do I?  Whenever I have a day off I feel that it should be spent running. I feel that anyone else training for the same is doing just that. Running for hours and hours, day after day and being disciplined with diet and everything else that comes with it. But I am finding that I am battling with guilt of not doing enough, not knowing if what I am doing is enough and whether I really have it in me. I know that's all part of it. Seeing how much you are actually willing to push yourself and grit your teeth and get on with it. Well, it's really testing me!!!
My mood has been particularly low, to a point where even running is a chore. I feel mentally drained and the pressure to get in the miles is not helping. I continue to compare myself to others as a way of seeking reassurance but it fails as all I see is them doing more than me. So I am going to continue to do what helps me mentally and hope that with it my energy and psych return. I may not be doing 40-50 mile weeks but if I can walk, cycle, jog a bit and just keep active, as I always have, and enjoy it, I will have to hope that there is enough in me mentally to get me through.
P.S. Please feel free to comment, ask questions, discuss etc etc :)