Writing without sarcasm

I'm not used to writing without the slightest trace of humour. Sarcasm, hyperbole, cynicism, irony, it's all there usually. In my new novel, however there's no chance of humour, unless it's of the gallows kind. I might be able to work some in later but at the moment it's all bleak. I wonder if people will read it long enough to get to any lighter moments later on without leaping off the nearest cliff or jumping under any passing truck. I like writing humorously. Other people might not find my stuff funny but I do. My wife thinks I'm completely strange and has suggested that I seek professional help. I told her that's what I should have done after I married her. It didn't go down well. Can't think why.
  I'll keep going, though. It's interesting if only as an exercise. Though I'd probably best get rid of the cut-throat razor that I keep in my desk to sharpen pencils. It might be catching.