Fraser Milton

Aphantasia is not the sort of thing that you would get a doctor to diagnose. It is different from most other things because there is not a clear objective means by which a doctor could definitively diagnose aphantasia as they don't have insight into your imagery capabilities. fMRI/MRI also would not work as there is not a clear neural marker, only characteristics that one can observe averaged over multiple people. At the moment the best and most common way of establishing aphantasia (and what researchers in the field do) is take the VVIQ https://aphantasia.com/study/vviq/ If you score 1s for everyone question you would have what we call extreme aphantasia (a score of 16 overall on VVIQ). 17-23 moderate aphantasia and 24-32 a mild aphantasia (or dim imagery). It may be in the future clear neurophysiological markers are established that can lead to a more "objective" diagnostic criteria but for now this is the standard way of diagnosing it and one doesn't need a doctor to do it.

Yes that is quite common for episodic autobiographical memory to be down in people with aphantasia which is consistent with the idea that this sort of memory taps into visual imagery to a greater extent than some other types of memory. I think several studies have objectively demonstrated such a pattern although the reduced autobiographical memory is definitely short of what people would typically consider as "amnesia". Your observation about struggling with maths equations or other sorts of semantic memory is interesting though as this typically is thought to rely on imagery to a lesser extent (although one could argue that imagery is used specifically for recollecting the equations. As far as I'm aware no one has looked at the ability to recollect semantic memory in the form of exam or exam like content so far in aphantasia so we don't know if it is a common trait or not at the moment.