Hey, thanks for the feedback! I think that's a pretty solid idea. It'd definitely encourage players to use cards on bosses more often, which is a plus. I'll look at getting that into the next version.
Oh! If that's the issue you're having, you can actually reset your discard pile for 100 Energy by hitting 'Q'... I think there's a tooltip that shows up regarding that, but it very well might be bugged in some cases. Sorry about that! Hopefully knowing that makes it more fun :)