Take a deep breath and calm down. Post-docking for 5 years should be enough, and if you really want to switch fields, then you can always go elsewhere.
There is a hard cutoff of 5yrs for IRTA fellows. I start as one in July (yey!). During my interviews, it was explained to me that as the NIH is a comfortable place to be, PhDs tend to delay their own career progression to stay there longer. The NIH limits post-doc time to facilitate booting 'young' scientists from the nest, or something like that. There are a few mechanisms that allow you to stay longer. If your lab transitions you to a staff scientist, then that's a different classification and is okay. I vaguely remember running across some "amazing genius" program that will also allow you to stay longer - but it's limited to very few people (like under 5) and you have to start out in it. It's easy for labs there to get post-docs, but difficult to get the okay for full-time employees (techs, staff scientists, etc). So unlike academia, where it's almost a sure thing that you can continue in your lab as a "research associate scientist" or some such business once your post-doc fellowship time runs out, you shouldn't plan on the same indefinate employment at the NIH.
