writing a mystery novel

I am working on a mystery novel, amongst other things.  I've been working on it since last year, but with lots of time off while I worked on other things -- or simply didn't work on anything.  

I've written more than half of it, and I even have ideas for a sequel, if I decide to write one.  

The story is a mystery, and will be my first full-length mystery.  

I have the plot pretty well figured out.  A problem now is finding the time to write, and something else -- the conviction, and emotional energy.  As the story nears the ending, the pitch or intensity increases.  It takes energy to sustain that.  

I often have to pick my writing times by the mental energy I have.  Near the end of a novel, I frequently have to take into account my emotional energy as well.  Plotlines intersecting, things coming to a head -- it can take more out of you than the beginning of a novel, where everything is open, and you're doing it all for fun.

Plus, as you near the end of a novel, sometimes you begin to realize you may be saying goodbye to these characters -- and hello to a long, uphill battle of editing and submitting the story.  Which can be offputting, to say the least.  Exchanging the soft, left-brain activity of writing about people to the often-stressful, right-brain activity of second-guessing yourself while editing.  Not the most fun thing, believe me.