I've had this bug a few times, I burn through my entire stam pool in a matter of 2-3 casts, then I am allowed to cast things as long as I don't have 0 stamina, it could be like 60 stam in my pool and I can cast a 4k Magika costing Wall of Elements. Not only does this completely mess with sprint, block, dodge, and bash, but until regen ticks I'm literally worthless. Idk what causes it, idk what fixes it, but it's annoying and seems to happen in vet dungeons and trials where resources REALLY matter.