It sucks. It's common. It's scary.
It shouldn't happen.
But it does.
I'll give you an example.
So last night, I was happily typing away the end of my story, watching my word count grow and trying to keep a somber mood to match the story's current tone. I was very absorbed in my world; I didn't care that my AC was broken, it was 95 degrees, and I was sitting on a leather couch. I had a fan. My mom told me to open a window, and I mumbled, "Why don't you?" Which, of course, made her turn off my fan and leave. Did I jump up and turn it back on? Nope. I just kept typing while I slowly suffocated/dehydrated.
...Until something bad happened. Not in my story, but with my story. I came to the realization that while I had been making my very detailed plot, I had kind of skimmed the ending and didn't take in to account a few very important matters. Which led my characters to neighborhood I didn't know existed and to a building I haven't designed.(I make floor plans for all of my buildings.)
As soon as they stepped inside the mystery building, my imagination flat-lined. I couldn't figure out how it was supposed to look to be productive in the story. They were supposed to meet a character in there, but I didn't know where she was. I didn't know where anything was. I couldn't even finish a sentence.
So, I calmly stepped away from the story with my hands on my head. No harm, no foul.
I stopped thinking about it, took out a book, and went to bed.
Today, I opened my manuscript up and didn't try to finish that sentence. I didn't even waste a second looking at it. I scrolled back up to where I had been before I'd gotten lost and pulled out my map (AKA plot). I drew a floor plan. I re-read my plot and added the details I'd forgotten and changed the stuff that needed innovation. (Sometimes the problem that has you stuck could be in what you've already done.) Once that was finished, though, I didn't continue writing immediately. I took a walk. I started a new book and payed extra attention to how the author described things. I put in an awesome movie with great dialogue and an epic story. (Pirates of the Caribbean, of course.) I soaked in new wisdom and doodled a bit. I let other people do the thinking for me for a little while.
Then I looked at my story and deleted the evil sentence, ready to finish the scene with a refreshed mind.
Well, okay, then I made a cup of coffee because my eyelids are feeling heavy for some reason and wrote this blog post. (Sorry for any typos--the caffeine hasn't kicked in yet.)
My life motto is stuff happens. I don't dwell on the small things that have no solutions. I don't let myself freak out. Stress makes everything worse. I stay calm, take a break. If I can't think of something at that moment, I shouldn't keep trying think about it. I distract myself with different activity. It always comes to me in due time. The world won't end. Not when I have an unfinished manuscript. The sun will come out tomorrow.
So what about you? How do you deal with writer's block?