"an unbearable feeling in my throat that is hard to explain, it's somewhere between pain, vomiting feeling and a sensation of it closing".
As long as you are drinking water-only according to thirst, and nothing else, it is possible that your exercise routine may have a strong bearing on the matter.
Fasting is known as "the rest cure", so the next time you fast I would personally omit any exercise and see if that helps with alleviating your symptoms.
It is also possible that you may have psychological feelings such as anxiety that are re-surfacing while you fast and which may also contribute/cause the symptoms you refer to.
I am not aware of any underlying physiological reasons that are causing them.