drowning in the deep, dark sea
I've been thinking about what scares me, and I was struggling hard to find something just so I could post it in the OP to kick things off.
I'm not scared of insects (though if one of significant size lands on me, I might go a bit crazy for a moment). I actually think spiders are cute and always carefully put them outside instead of killing them. I can't help feeling they are a degree above other creepy crawlies and get too much bad press. They make webs that catch the pretty dew, keep the fly population down too. Bees I like, they keep busy and mind their own business unless you wind them up. Wasps are just nasty little killing engines, but I'm not scared of them. I want to punch them.
I'm not afraid of reptiles. I've owned several lizards. I'd prefer a dog. I'd LOVE a dog. But it'd be cruel to leave a dog in the house all day alone. So lizards are a great choice. Requires no expensive filter system and constant cleaning/maintenance like a fish tank. Plus I handle live food (grasshoppers, crickets) so I'm not afraid of those either.
I'm not scared of the dark. I mean, I have a healthy response to noises in the dark, or movement, and a working adrenaline gland. I have what I assume to be the common instinctual reaction to potential danger, etc. But I'm not afraid of 'the dark'. I like the dark.
I'm not afraid of heights. I have a healthy balance and orientation trigger that kicks in if I'm in a dangerous high point, or feel a gust of wind when I'm up high, or lose footing, but if I'm safe I actually really enjoy high views. We jumped off of some mega high waterfalls in the Dominican Republic. Done bungee jumping, a bungee catapult, paragliding, helicopter ride. I loved every minute of being so high. I love flying too. But only with a window seat.
But what you mentioned there - the deep, dark sea - is one thing that gets me. I don't mean shoreline, looking out to sea. I don't mean being out on the ocean per se. I love standing out on deck on the ferry to Amsterdam. I think I look forward to the ferry journey more than the coffee shops. I'm a regular swimmer. I can swim out far, or on a lilo, a pedalo, or jetski when on holiday, and its only really exhaustion that makes me want to turn back. I can surf, albeit not very well and can't claim to have surfed any big glamorous wave or anything like that. And white water rafting is one of the most amazing things I've ever done.
Water in general isn't what gets me. What gets me about water is those deep ocean swells you sometimes see. Where a massive yawning valley of water will appear, or a huge lurching mountain of it. I even get a gut tingle when I see it on TV and a slight tinge of despair. Just the idea of being isolated in the middle of the ocean is something that genuinely scares me. If I was alone in the ocean, caught in a storm with those black miles of liquid beneath me and that churning, rolling surface, I think I'd actually go insane.