I'm not overburned with weight, and I'm not stealthing, but suddenly my character is walking like a snail everywhere I go. And pressing Alt to sprint doesn't do anything - literally. I've even remapped the sprint button and it still doesn't break into a sprint when I press that? Is this a bug?

I've tried pressing every button (I think) on my keyboard in case I hit like an "always stroll" mode or something but that doesn't seem to work.

Frost magic does this to you. Been in a fight recently?

Look on options/controls for a key binding to run

A,lso go to magic and look for spell effects to see if you have some sort of disease w hich you need to get cured

:D

The always walk/run mode key is Caps lock for PC, but it sounds like you probably tried that already. Have you tried just restarting the game?

Doesn't some shout cause this to happen? I think it is a bug.

Oh, yea there is an "always run" button. For me it's Q but I have no idea what the default is (caps?). Just look under controls for always run and see what it's mapped to. Keep hitting that button until your character starts running.

there is a keybind issue or bug, unless you are being stricken by certain mob leader/boss spells.

I've had this before also. When you go into items and back again it should be gone.