You are not alone. It appears that some fears are built into our brains from birth. Studies of infants have shown that they are inherently afraid of 3 things: Heights, Spiders, and Snakes. I'm pretty sure this fear may have something to do with the serpent in the Adam and Eve story.
Once you had that snake image rattling around your emotional centers, your hippocampus took over and just about anything could trigger you.
We once had a pool that was surrounded by brick pavers, except the guy we paid to install them did a crappy job with the subsurface prep (no gravel or marble dust, only sand). Rain would wash out the sand and brick would start sinking, so I'd always be fixing it. Getting the first brick out would often be tough. One day I was pulling with all my might and when the brick came out, a huge snake literally burst through the hole scaring the cr@p out of me. It was really hard to do those repairs for the next year and the memory is still strong.