So no one else gets that uneasy feeling? The excitement, the fear?
All. The. Time.
I'll give you an example that's pretty darn similar to yours. There's a local lake about 40 minutes from here where I have started doing practice dives. The viz is universally poor: 15-20 feet. There are things sunk on the bottom: a small cabin cruiser. A platform. An elevated oil drum. And more past that. And they're all in 25 feet of water, no more.
I've dove this section to use the platform probably a dozen times or so. In swimming out, I get to the items in the order listed above. And I know that I will get totally spooked out by each and every object as I come upon them.
It's that period of time leading up to them resolving in front of me. At first, there's an ever so slightly darker patch, that grows and develops over 10-15 seconds until eventually I recognize it as the object. I am seriously creeped out during that entire time. The bigger problem is, an ever so slightly darker patch isn't *always* the object: sometimes it's just a change in depth or bottom contour or bottom surface. Yet every time that happens I get the creeped out feeling.
And it takes *several* minutes to swim out along the shore to where the objects are. So that's *several* minutes of being on that line of fear.
I hate this. I hate this *so* much that it's the swim out to the platform that is the single biggest obstacle to me using this lake more often. I just can't always make myself put my gear in the car knowing that this is how it will go.
What makes it worse is that the platform is between the cabin cruiser and the oil drum, and both are *just* far enough away that they don't really resolve into objects. So, if I swim around the platform, I'm constantly presented with those half-resolved objects just beyond my vision.
I find that this is much worse when I'm diving solo (as I tend to do in this lake, as nobody else wants to spend an hour swimming around a platform in 65 degree water with 15' of viz). With a buddy, the creepiness is still very much there, but to a lesser level throughout, especially once it's resolved. (I'm still creeped out by 100% solo diving, so basically my margin for creepiness is much lower when solo.)
The first time I experienced it I was diving with my daughter in a different local lake for the first time. We were following a line which took us to various objects. The first object was a boat sitting on end. Same thing: major creepiness as this dark, looming object resolved itself, then momentary huge spike of fear as you realize that this is a boat on its end -- and it's going to fall on you now! Half a second to realize that no, it's just fine...
It was funny: I was leading my daughter, and I screamed when I recognized the boat. A couple of seconds later, *she* screamed for the same reason! Good (?) times...
A few thoughts about this:
For me, it's the low visibility that does it. I've noticed I get a much lower version of the same feeling as I descend on a wreck. Looking down, it's blue and dark, and then slowly it gets darker, until a hazy outline appears, and then I relax as the details of the wreck resolve. It's worse the darker it is (like Great Lakes dives), but because it's farther away (maybe 40-50' instead of 15), the feeling of impending doom is much less.
Also, repetition is not really making that much of a dent. Like I said, I've done it a dozen times, and probably 6 times last summer alone. By the end of the summer I was better able to recognize it and put it aside, but the level was not really less: just more expected. Mental preparation has helped to address it, but doesn't reduce it.
Also, I do *way* creepier diving than this. I'm a baby Full Cave diver, with maybe 20 dives of >1000' penetration into caves. I've been doing wreck diving in Pompano and Lake Huron for a decade, and I've wiggled through various kinds of restrictions deep into wrecks. Sometimes I'm alarmed or concerned, but *never* with that same feeling of deep, uncomfortable fear that I get from a perfectly harmless 25' open-water environment 50 feet offshore...
Exactly the same as what you're experiencing? Dunno. But yes, there are perfectly harmless situations that will put a massively uneasy fear in my head. I mentally know what's going on and that allows me to continue through it, but even with that, I'm not able to actually reduce the actual uneasiness, just address it.