You cannot change the difficulty once you've started a game, sorry.
The bars will disappear once you've rested at least 12 hours allowing the area to reset.
As for that quest, walking over spike traps like that happens. All I can say is be more careful in watching where followers are in relation to you. If you want to make that quest easier, there is a secret passage that cuts out the area full of skeletons and minimises the number of enemies you have to kill.
Here is the map with these marked on:http://www.exiledkingdoms.com/wiki/inde ... Nayau_Tomb
If you're having trouble detecting secret doors, then use a scroll of detection.
One final note, if you're having trouble in an area, you may want to look at your build and equipment and decide if something needs changing. Sometimes, it's worth coming back to an area or quest when you've leveled up. I would also recommend to new players to buy an extra recovery with their skill points, it will allow you to travel much further without needing rest.
Finally, don't be afraid to use potions and other consumables like scrolls. A lot of players hoard them and never use them, it kind of makes them useless.
Too bad, I expected it somehow. Still it's good to know the library is just a reset issue.
About the quest, I found that secret door before I fight the boss, and that lady step on a spiketrap just near the secret door, it's kind funny now when I recall that situation. And indeed I died a lot to that room full of skeletons, but only because they stuck at the door and start to rapidly regenerating, making most of my spells wasted, if they don't always stuck and regenarating I can clear that room quickly by spamming rank 2 ice storm. Last, don't worry, during boss fights I chugged like I was playing Dark Souls XD