I go through Lulls and Highs like that in Numismatics,
Everyone does, Maybe some
more challenging Classic U S Coinages,
Commemoratives, Classic -1892 to 1954 , Modern - 1982 to date.
The Lincoln Cents, 1909- date.
Walking Liberty Half, 1916-1947
Franklin half, 1948-1963
The
Kennedy half, 1964- to date
Proof sets1936 - to date.
Mint sets 1947 - to date.
Special mint sets, ie, The all Black boxed Silver Sets1992-1998, Premier Silver sets, etc.

Original
Morgan silver dollars, 1878-1921 a series with-in a series are the
Morgan silver dollars in the GSA Boxes,

Some are certified, Most are Not.They are Highly coveted and collected, Some awesome Deep Cameos, Deep Mirror Proof-like examples, Very Sweet tasks.
Original Peace Silver dollars, 1921-1935.
VAMS, The study of Morgan and
Peace dollars, Die breaks, Clashes, Letter transfers, All highly addicting and Rewarding that reveal knowledge of the intricacies of the Designs .
These suggestions are full of challenges to Any Coin Collecting Numismatist/Enthusiast. I collect all of these in Original Government Packaging, all corresponding literature and boxes.
How about Chinese Pandas, Just watch the fakes.....

Most bought on the Bay, Decades ago.
I personally reviewed Thousands of Peace and
Morgan silver dollars, Best reading material I have found for VAMS is the Comprehensive Catalog and Encyclopedia of Morgan &
Peace dollars, Fourth edition by the Founders of The
VAM formats seen Today, Leroy C. Van Allen and A. George Mallis, It's an Addicting adventure, Best Wishes...