How does regaining my Vigor work?

Part of my problem with combat in The Witcher 2 currently is that I'm unsure how to react when I run out of Vigor, as I'm not sure what's required to regain it. Can I simply run away from my opponent and hide in a corner to recover it, or must I attack to regain vigor?

By default, you regain Vigor in combat albeit slowly. By bringing up the character stats page (default shortcut is 'c'), clicking "attributes", and then browsing to the "character abilities" tab, you can see many things, including your Vigor and Vitality rates (in combat / out of combat for both).

Specifically, Vigor regens at 1/3 of the rate in combat as it does out of combat (before modifiers)

Finally, you can't regen Vigor at all when you're under the effects of the Quen sign. (I have a feeling this might be your case).