Are you getting stuck on an object by any chance? specifically walking into a map that is generating still?
That seems to be the most common, otherwise not being able to activate things can be solved by pausing and unpausing.
as usual, if you're experiencing a bug, it helps to know what you were doing when it occurred.
Are you sure your legs aren't being broken? and are you picking up to many objects?
1. Being attacked by large enemies like bears, and being hit by blunt weapons (Club, Mace) can result in broken arms and legs. A broken leg can slow you down greatly, you'll know the leg is broken by a red icon near your health bar or by pausing and checking the left side.
2. You might be carrying to much stuff. Your backpack has a weight limit before it slows you down.
