Pretty self explanatory- my follower isn't attacking properly.

I first noticed this when making my way through the dwarven ruin Mzulft. My follower, Marcurio, had stopped attacking enemies. His hands were in the correct position for spellcasting, but they were empty. The problem did not resolve even when I gave him a staff and a sword- he was still empty handed. He just stood there helplessly until I finished off the enemies myself.

The only thing that fixed his attacking was going through a loading screen door. When the game loaded again he took out the sword and began attacking enemies with this and his spells again. I don't really know what caused this glitch, but I think the problems started when Marcurio was knocked to the floor and staggered upright again.
This isn't the only dungeon/area it happened in. It also happened in Labyrinthian, and in the wilderness near Riften. (Though I can't see why it happened in the wilderness, as he wasn't knocked to the ground.)

It's very annoying to have a useless follower until the next loading screen. Has this happened to anyone else?

That can happen if you overload your follower with (literally) tons of dwemer metal.

Edit: Had to cut my post short to eat dinner. Here's the rest of it.

Your follower can be exploited to pick up any valid object, even after they reach their weight limit. I'm assuming this is what you did. I do it too, in the dwemer ruins. Sometimes my follower will lose the ability to fight because of it, sometimes she won't. And you're right--going through a door to a different area that has to load will fix the issue. I see it as fair. If Lydia is carrying dozens of those heavy struts and solid-metal blocks, she shouldn't be able to fight very well. So it doesn't bother me too much.

becareful overloading your follower,i did it to much and the items vanished from their inventory and was now at their weight limit for all time even with an empty inventory,i also read somewhere in a forum post about it happening but didn't stop over loading my follower till it happened to me.

Hmmm, I see your point and why that might affect them, but I didn't give him anything. The only items I gave him were a novice hood, orcish sword and a staff. I didn't even give him any junk to carry- I try to limit the amount of stuff I cart around to enhance my immersion.

I might take everything away so he has only his default items and see if this makes a difference, and try out some other followers.