If you compare video clips and photos of the Congressman now and only a few years back it appears that he has aged considerably. He is obviously not well. Chronic liver failure - as a consequence of Hep B - can cause encephalopathy, and as you pointed out interferon treatment can cause a number of cerebral symptoms, where the most common side effects appear to be depression and an acute confusional state. The latter develops rapidly after initiation of high dose interferon therapy.
I just have to repeat what others already have asked: How sick and confused can you be and still be allowed to vote in the Congress? And what is this man’s staff doing?
Collecting paychecks from the taxpayers.