History is like that. One day you can’t get enough of WWII culinary skills, Ancient Greek composting, or the Thirty Years War and the next day… nothing!
Historical curiosity travels in phases. While a particular subject can really never be worn out as an area of study, it can wear out in our minds. We get sick of hearing, reading, or thinking about it. At that point some even give up on history (even us nerdy historian types!).
Fear not! It isn’t necessary!
I will call this (since I’m writing here) the Law of Historical Opposites. It’s actually more of a technique, but “law” sounds more impressive.
Flip your area of interest. Love Prairie Cooking in the American West, but are sick of recipes for Johnny Cakes? Try reading about Native American tribal history or the manners and customs of the American East or of Colonial California!
Have always liked the interminable accounts of the WWII European Front action, but simply need a change – then search out Pacific Front histories or leave WWII altogether and pick a different war. Humans being what they are, there will never be a shortage. Or, the ultimate flip, search out the history of Amish and Mennonite pacifism!
Keep it fresh, and you will always stay curious!
– Amanda Stiver
History Gal 
That’s a good technique to follow. I try to keep fresh with reading–right now I’ve been reading a lot about the history of water development in the West and music history, and pretty soon I’ll look at some more Civil War histories to keep things fresh. Reading broadly with regards to history also provides one with a great deal of context and keeps one’s perspective balanced.
Good advice indeed. Reading outside your research area gets even harder to do while writing your dissertation. Sometimes I find myself so enmeshed in my Pacific world that it is hard to escape. I’ve been reading popular histories (and fantasy novels) to do so.