Yeah, the Jill/Kamala hatefest is a whole other problem for the Dems.
The whole Biden has COVID19 (again!) is not likely.
He is experiencing stress, exhaustion and depression from a whole two days of campaign travel with very brief appearances and botched softball interviews. He is recognizing his failures.
This depression is a component of his increasing cognitive decline combined with his self-aggrandizing, self-absorbed, vain, ego-driven narcissist personality.
Once he learned that he could get away with the egregious drunk driver lie decades ago he found that the media would give him a pass on any falsehood that he continuously told. That realization of the end of ongoing free-pass is hitting hard with the cognitive issues.