3. Brain Fog
When you reduce the amount of oxygen you have in your blood this can hugely affect a number of different operations around the body. In particular, this can negatively impact your brain function seeing as the brain is one of the most energy-hungry systems in the human body. Without the brain getting enough energy, patients will not only feel tired but they may also experience brain fog, meaning that they can struggle to hold their concentration on one thing for long.
Kidney disease can also cause headaches for the same reason and even low motivation.
Note that brain fog is actually a symptom of many conditions once again. In particular, it has been commonly linked with depression and stress and this in turn might be the result of inflammation in the brain at least to some extent.