The more valuable you are to your company, the more likely you are to be viewed as a cornerstone of the enterprise. Check your value against the measuring stick of profitability. You see, profitability is at the core of every decision to downsize. It's rare that a downsizing leads to a complete business failure. Companies don't just go out of business when they lay people off.
Cutbacks reduce cost, and that contributes to health.
Make sure you understand where your division, your product, your project, your department and your job fit into the profitability scheme. While you probably won't be able to come up with exact numbers, it's important that you try to calculate whether your work is costing the company more than it's yielding. If you're in a questionable function, don't be a sitting duck. If you can explain how your work is profiting the company, you've got leverage. Make sure your employer knows what value you add to the company's bottom line, no matter what your job is.