It is very important to understand the difference between a high dynamic range image, and a high dynamic range image that has been tonemapped back down to low dynamic range for display on a standard monitor.
This is a high dynamic range image that has been produced from multiple exposures:
Looks dull and lifeless because you're viewing it on a low dynamic range monitor. What you can do is locally adjust the contrast, so as to maximise the dynamic range of your monitor in every part of the image. This process is called tonemapping:
If you've done this tonemapping step (which is easy to detect as it makes your images look like the above), then you're out of luck, you'll never get back to the original(s), as it's a highly nonlinear filter that takes whole neighbouring image areas into account.
However if you've merely done a merge-to-HDR-image, then that process is entirely reversible, you can get back any of the original images by just truncating the dynamic range at the appropriate points: