when i was sneaking in Blackreach, i turn around, and there is a [censored] load of falmer and charus after me. i screamed so loud, my parents came up stairs... lol

The wolf snuck up on me.

Nothing gets scarier than that.

Three words: Undead invisible dragon

I saw a mudcrab the other day...

I'm sorry I had to say that. On a serious note, I would have to say the first time I encountered a Chaurus and I could hear it clicking around, and I was like, "What the [censored] is that!!!!"

When I kept crashing every time I tried to save. Scared the hell outta me.

In-game, no, I don't really get scared at games. Only game that legitimately scared me was Amnesia: The Dark Decent. I don't know why... Just the feel of everything combined with how helpless you are is creepy as hell...

On my first playthrough, with the lights out and my headset on at about 2am. I was wandering through Harmugstahl. I'd slaughtered everything and was having a nosy around. I went into Kornalus' bed chamber and on his desk was a dead frostbite spider, cautiously I walked around the table and looked at the shelving to the left to see if there was anything worth looting. Suddenly I heard a noise and the leg of the dead spider that sat on the top of the unit dropped down. I screamed, and it was loud!
Every time I go through that dungeon now, I launch several arrows into whatever seemingly dead spiders I see... Just to make sure.

Absolute scariest moment in Skyrim was when my Honeyside mannequins moved.

I havend got a single scary moment in Skyrim - 608 hours played.. but i had in Oblivion for sure, was about to piss myself on that ghostboat the first time i was there and the sounds was scary =)

First climb to High Hrothgar. Dusk and heavy snow, could probably see about 8 meters in front of me. And all of a sudden, there's a Frost Troll.

Dwemer ruin, elevator, giant spider.

Oh hey, a elevator..... (rushing towards elevator)
Giant Frostspider out of nowhere: "PIKABOOOO"

Normally i do not fear them but this was just unexpected.

I was in Proudspire Manor and saw a bear eating my Sweet Roll Collection (Nah, not really. I do have a sweetroll collection and was pissed when Jordis destroyed the arrangement)
I was in Proudspire Manor and the decapitated bodies I have in my basemant failed to load properly and looked like they were standing.
I was in Proudspie Manor when a Mannequin appeared in my room and I thought it was Slender Man.
A courier appeared naked and said "I have something to I'm supposed deliver, your hands only".
Kagrenzel's Falling Pit
The ultra large Chaurus Reaper at Frostflow Lighthouse
Cicero saying "I have to oil night mother in those "hard to reach" places"
Failing a pickpocket and Cicero saying "Looking for my juggling balls? He He He"
Getting in Night Mother's Coffin (creepy as hell)
My first time a Centurion ambushed from the back. Automatons tend to attack you when your guard is down.