This is like a detective story, where the author follows the bread crumbs, leading up to the ultimate discovery of a brain tumour. I too follow such clues in my own life as I try to make sense of myself and the sometimes puzzling world around me.
The symptoms included a rumbling sound in his ears, which anger or irritability seemed to trigger and he interpreted as being a train in the local vicinity; more likely though it seems it could be caused by blood pressure, which I sometimes get, with ear canals blocked with wax. In other words this is not so much an hallucination as he believes but internal, bodily phenomena. The problem is interpretation over identification (what something reminds you of as opposed to discovering what it actually is - memory and imagination as opposed to present perception).
One of the interesting things this book discloses is the apparent distance and direction a sound is coming from. What we may mistake as being loud and far away, could in fact be much closer than we imagine, internal even. The book is therefore asking, can we mistake inside sensations on all sensory levels, for external ones and if so, what are these clues trying to tell me?
Other symptoms included giddiness, connected to fainting fits, nausea followed by vomiting, leaning to one side and as the illness progressed, eyesight and handwriting deterioration. He also suffered from headaches, which eventually became focused on the back of his head. One subtle symptom that seemed to creep up on him was a gradual loss of taste, like Covid patients nowadays but with no loss of smell. After the operation, he regained this lost sensation.
Apart from all this, he starts getting unconscious clues to the fact that something serious is going on in his life, through dream symbolism or even external events drawing his attention to the same thing (films on the subject, a dying patient in a mental ward etc). By monitoring his life, he starts to build up a picture of what is really going on, with his illness and that it is indeed an illness. Something out of the ordinary was happening internally, just as it could in the outside world, disturbing the peaceful routine of existence but the question was, what? Like paranoia from chronic insomnia, you know something is killing you but you don't realise what it is.
I for instance have two common dream themes, one which is needing a toilet but not being able to find one, which wakes me up as a symbolic prompt, to get out of bed and urinate (being a seventy year old male, this is par for the course). The other repeat pattern is finding myself at university or on the outskirts of one, which is because I am continually seeking knowledge and insight to the human condition or indeed anything. Like Einstein I have no special talents, I am just passionately curious. I did in fact live in Cambridge but never studied there or indeed at any university.
Another thing this book discloses is how previous knowledge is built upon and refined through experience, so that over time human awareness, human science progresses as more details about reality are discovered. In this way, the darkness of ignorance is pushed further away by the light of truth, highlighting the previous errors of thought, buried in history. He also mentions the tempo of impressions we all have for measuring time, citing HG Wells Time Machine: we live in the present but measure time as change, which Walter Pittman of Gettysburg College also points out 'What if all truth is just an experience of consciousness?'
In chapter thirteen, we hear how a young, enthusiastic surgeon wanted to ride to his rescue, trampling over him in his certainty. Instead through his own knowledge of surgical procedures and their outcomes, he was able to save himself from this well meaning interference. This lack of knowledge by the young man then could have killed him (see Dunning - Kruger effect and overconfidence): apparently the body collects poisons in cysts and by cutting into them, you release them back into the patient, killing them.
When the author is in a clownish, entertainer mode (dispersed mental state), he allows his terse observations to be dismissed by the opinions of others - in other words social popularity overrides personal awareness (experience) of the truth.
This is Eastern Europe, sounding like the eighteen seventies, not the nineteen thirties. The narrative is in some ways like the ramblings of a senile old man until you realise that this is the crumbling remains of the Austro-Hungarian empire, pre-world war two. It may remind you of a Pirandello play or Alice down the rabbit hole, in its confused interplay of ideas or the insane babblings of the Mad Hatter's tea party. More probably though the slightly sinister feel to the story, may remind you of some Kafkaesque nightmare as in The Trial, through its subtle paranoia sitting in the background but maybe that's the disease at work and not the society of the time.