what were the disease of the 3 friends?

The reader can discern that they are actually hypochondriacs. After researching diseases at the British Museum, J. has recently concluded that he suffers from every disease known to man except for housemaid’s knee. As for the other two:

Harris said he felt such extraordinary fits of giddiness come over him at times, that he hardly knew what he was doing; and then George said that he had fits of giddiness too, and hardly knew what he was doing. With me, it was my liver that was out of order. I knew it was my liver that was out of order, because I had just been reading a patent liver-pill circular, in which were detailed the various symptoms by which a man could tell when his liver was out of order. I had them all.