Oh, you mean an inner page? I don't think that's so abnormal, but how long does your ranking drop off?
If there aren't any links pointing to your inner page and your root domain isn't highly authoritative, it's not very likely any of your inner pages would maintain a rank as well.
Edit: I forgot to mention, if you want to rank an inner page, build some links towards that page too. I mean you should be doing that anyway just to maintain links throughout most of your site to look "natural", but you could focus more links on specific pages you want to rank.
Also, I'm not 100% sure if this is still a viable method since I'm a bit out of date with techniques, but you could also try interlinking pages between your sites.