I see nothing onscreen to give the impression that being chained up for 175 years was not a horrible, unbearable experience. I see no reason not to think that he awakened every night and had to pass that time conscious, until becoming dead again at sunrise. Vampires can deal with going into the coffin every day, yes, but that's because they become unconscious and inert (in other words, a corpse) during the day, and anyway, going into a coffin every day is a LOT different from staying in there for 175 years. Imagine it. Being afraid of that isn't claustrophobia, it's just basic sense. No wonder Barnabas came out of the box psychotic, in 1967. It's a wonder he could control it to the extent he did.