Actually, I am VERY familiar with the feeling. It's a very bad sign. It means that you are not hunting for enjoyment right now but rather as another job. Something that "has" to be done. You know, like school? Work? Taxes?
I'm semi-serious about this. When I get this way. Where a find that should excite me to no end and it just barely registers. Well, it's time to break. Time to stop going and not go back until that familiar little anticipation for going, returns.
Getting on here doesn't help the feeling much either. It can actually cause it because we see rare and very hard to find things here EVERY SINGLE DAY! So, unless it's "banner" worthy, we feel like, what's the use? Another Wheatie, Rosie. Or in your case, "Just another large cent." (HO HUM).
Understand?
Do a little research, find somewhere that really interests you. Then, wait until you REALLY want to find and go again.
Another thing that helps is to go to the single trashiest place you know of and force yourself to dig for a couple hours at least.
HH!