Not mentioned but worth considering are also mental illnesses.
If a sensitive/magically latent person is bombarded with too much "information," they could first display mental traits--feeling imaginary presences, inability to handle stimuli, sleepwalking, nightmares, or even more extreme in splintering personalities, mood swings, etc. Even if you don't want your disease to be purely mental, it might make for some good first symptoms and/or a way to distinguish the "magical" disease from more prosaic ones with similar symptoms.
Hypersensitivity is also an interesting one. In real life, this could briefly appear due to stress or anxiety or be something one is born with and deals with all their life. Basically it's when all your senses are more heightened. If born with it, it's usually normal to the person, but is noticed when they start comparing their experiences with those around them. Those with good noses also have the tendency to be called upon frequently by friends and family to "track a smell down." Smell can also effect them greatly, with scents being so powerful they can make them nauseous, dizzy or light headed, or even throw those who are prone to it into a migraine.
I have a friend who gets drugs intravenously for her MS, and she can actually feel them spread through her system, and even taste the difference. The nurses actually tested her once, had her close her eyes and wouldn't tell her which drug they were giving her. She identified them all correctly by taste. Not that it's all that pleasant for her--the nicest tasting one tastes like Windex.
For myself, I once had fun with hearing. I worked at my family's video store, and they had one of those industrial ice cream coolers brought in so we could serve ice cream. Almost as soon as they powered that sucker up the most godsawful chirpy-screech started sounding, high pitched and just awful. There was no escaping it either, it bounced from wall to wall and could be heard all over the store (don't think Blockbuster but a small-town video store with multiple rooms in a converted building). It hurt like a ice pick through my skull.
I begged them to let me leave until the machine was done gearing up, but they didn't believe what I was experiencing and made me stay. I mean, no one else, staff or customers, were having any issues. It wasn't until they found me cramming my body as far as it would go into a corner on the far side of the store with my face dead white--somehow the sound bounced so it missed that corner if I stood
juuuuust right, and I didn't even realize what I was doing until I was caught at it, I just wanted to escape the noise--that they finally acknowledged something might be wrong. So my aunt, determined to get to the bottom of it, walked over to the machine and heard nothing. She circled it a couple times, then finally got on her hands and knees, and put her ear directly to the vent.
I never forgot what she said next, beaming from ear to ear because she'd finally solved the mystery; "I hear it! It sounds like a cricket!"
A different friend's child had a step up from Hypersensitivity, though I don't recall the name of what she had. I think it may have been Sensory Processing Disorder (SPD), though I'm not 100% on that (I recall her situation more than the name, he'd often vent to me about her progress). But what it amounted to was she had trouble living a normal life. Scents, sounds, tastes, everything was so overpowering that she often had trouble leaving the house. It took years of treatments and therapy before she learned to handle it.
One of the issues she had was she couldn't "block out" the way others can; for instance, if you were listening to music, in the background you might hear cars on the road, construction far in the distance, a plane passing overhead, a dog barking, and someone talking loudly on a cellphone in the other room. If you
focused you may notice all this, but you also have the ability to let those unimportant noises "fade," to shunt them aside so all you really hear is the music. Maybe also the cellphone, if they're being really annoying.
She didn't. She'd hear
everything, all the time. The same with smells, they never deadened for her, she never got used to them to the point she didn't smell them. Every touch was felt, every color seen, all bombarding her, all the time. It was a wonder she could function at all. On the upside, she learned to love hanging in her room and became a really smart bookworm and computer techie.
She presented as having emotional issues, mainly because the constant barrage of sensory information was just so intense and overwhelming she would easily lash out, startle, become overwhelmed, and/or break down crying. Sometimes in short succession of one another. She was a mess. And while it presented at first glance as a mental illness, it was actually very much a physical disorder.
To my knowledge what she has can cluster in families (it's kind of a recently discovered thing), and that tentatively implies it may be genetic, but if so it's quite recessive. Neither of her parents had it, nor could they think of a close blood relative who did, though there were possibilities a generation or two back, just judging by similarities in behavior.
Never underestimate what having heightened senses can do to a person, and it's terribly difficult to diagnose, even now. I mean, how can you prove what you see or hear or feel, or explain how different it is from those around you? As a disease symptom, that would be positively insidious.
