After droppin' Nastradamus, he disappeared for a minute. That album was critically panned and he kind of took a hiatus from it all. It didn't help that his most high profile features at the time was Monica's "Gotta Have It" from the Big Momma House soundtrack. Then he came with the "Oochie Wally" single from the QB's Finest album. Then there was the collabo w/ 3LW. He was featured on a few XXL Magazine covers and that was pretty much it until the beef.
I wouldn't say he fell-off, but the late '99 until Fall '01 was a very uninspired period for Nas. Who knew that he was cooking what would be Stillmatic on the low, which was originally Nastalgia.