If your GP didn't react to a hematocrit of 0,59 then, wow!

That's like a doctor not reacting to a blood pressure of 180/140.

When I had a hematocrit of 0,54 I felt it, and felt better after jamming a needle in my calf until I filled up a glass with blood. And 0,54 isn't even considered serious.
At 0,59 some of the side effects you have might be caused by this.
But not necessarily, my friend said he felt nothing wrong at 0,59.