Remember, IWM is having a contest: submit your 200-word horror story to us at litaplaceforstories[at]gmail.com by September 30, and you can win a free book plus publication of your story in our October issue! Details at that link.
Here's an older story I wrote; it's 250 words long but it'll show you the kind of thing that can be done in a flash horror piece:
Some Zombie Stories: 1
It was four days, maybe, before he realized he was dead. Or maybe four weeks. It might have been weeks, for all he knew; the dead aren’t good with time (he’d learned.)
Nobody at work noticed, and if his wife knew, she wasn’t letting on: she hadn’t stopped nagging him about his socks and they still had sex every day, or nearly, so things were normal, there.
Once, one of the kids – his daughter? his son? He wasn’t sure, that was another thing about being dead, it was harder to tell people apart all the time – had looked at him funny, which he attributed not just to knowing he was dead but to the fact that his skin was starting to peel off.
He worried he smelt bad but had no way to find out for sure, no way he was willing to try, anyway.
Another time, he hailed a cab, but the driver’d slammed on his brakes as soon as he’d said “59th and 1st, please.”
“I don’t give no rides to no damned dead,” the cabbie’d growled. “Think I’m freakin’ Charon or somethin’?”
But for the most part, things remained dully, mutedly, the same as they’d always been, or mostly, for each day was a little less vibrant than the one before it. He wondered if he would rot away entirely, and at what point he would stop thinking. Then he wondered what was for lunch, even though he was never very hungry anymore.