Oh please. The skeletons are a minor problem when you get used to them. Heck, creepers turn into a minor problem after you get used to hardcore. The only challenging-ish enemies you don't want to fight would be Ghasts, Blazes, Endermen, Mama Slimes, Magma cubes, Zombie Pigmen(When in groups), Cave spiders(THE ANNOYING POISON), Silverfish(I hate these so much), and for some people....regular spiders :D
Even the Enderdragon is really easy....that is after you go through the ugly process of getting rid of all the little health cube things. All you have to do then is side-step, shoot an arrow, side-step, shoot an arrow, side-step, etc etc.
But I guess that's not the point. I see what you're saying. It freaked you out because you thought you were on peaceful and got hit by a skele. Like Splotch said, double-check your mode. You most likely aren't on peaceful if you are getting attacked by enemies(besides wolves, which I'm pretty sure spawn in peaceful too, but they only attack you if you decide to "pet" them).
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