I was on my way to winterhold college when I came across a man and a woman on the mountains, I got them both to the ground, whimpering and stuff then i kept hitting them to kill them, but no amount of hitting would kill them, they'd just get back up again with full health... what the hell is this? i've also noticed loads of other glitches, the most annoying of which is when i was going to go down a waterfall and i got trapped in the current between the rocks, unable to do anything but fast travel to nearest location visited -__-

There are NPC's that don't die, they keep getting up. Its for a reason, they are probably important in some way to the main quest.