it is scary like being posessed or something...if u r looking for horror movies i suggets u start looking at Korean and Japanese horror movies...they are really scary ... other than that its really not that scary.
This ^^
I still remember how freaked out I was from watching the original version of The Ring, it was levels above the american adaptation which came later. So if you're looking for somehow recent horror movies that won't make you laugh out their special effects, better choose korean and japanese ones where the producers still give you that feel of crudity while other ones are too much graphical... don't know if I'm using the correct terms to convey my vision of it though.
Also, you should watch Drag Me To Hell, the approach is different here. The producers switch between humor and horror quite often, which makes you unprepared to any of them and therefore gets you genuinely laughing and freaking out when they happen... but it may be only me.