In my experience, exercise is vital to my mental well-being, just as the author of this piece found it to be for him, until he hit a slump.
We all hit slumps.
I hit a major slump when our child was born. Prior to that, I had been hitting the gym consistently (4 days per week), but my life changed and I had to re-prioritize.
However, where I failed myself is that I quit exercising entirely, because my "exercising world view", if you will, was gym-centric; that is, I had programmed myself to need a gym to be successful in working out.
I realized that I needed to change. After some research, I found P90X [1]. This is an exercise system (presented on DVD) that utilizes body-weight techniques (e.g., pull-ups, push-ups), yoga, plyometrics [2] and resistance exercises (you can use dumbbells or resistance bands - they demonstrate both techniques).
I also found a used Nordic Track ski machine [3] online for $100. This is not part of the P90X system, but I find it to be a fantastic cardio machine, and it allows me to change things up a bit... plus, the skiing action is fun.
The advantage here is that you can do all of this without going to a gym. Also, there is minimal equipment required; here is a picture of what is used in the system [4] (note the "Description" of the image that identifies all of the required pieces).
The system is fairly intense, but as with most things in life, you start very slowly and just work through what you can do, at your own pace.
I just wanted to share this experience, because I know we all struggle to find our routines, especially with exercise. I have found that one of the biggest challenges with finding an exercise routine is time: time to pack for the gym, get there, workout, shower up and head out. With a home-based system, you have essentially instant availability, no travel time and you never have to wait for a machine or piece of equipment.
[1] http://www.beachbody.com/product/p90x-what-you-get.do
[2] https://en.wikipedia.org/wiki/Plyometrics
[3] https://www.google.com/search?&q=nordic+track+ski+machin...