So my nord has been his normal height at the beginning of the game, but for some reason after I got done with diplomatic immunity, he is now shorter than other nords, and the same height as imperials and bretons. Does anyone know how to fix this?

Crouch then stand up? I know there is this glitch where if you are crouching and use an Alchemy Lab or an Enchanting Table and leave, you are smaller.

I believe there is some cake in Wonderland which allows you to get bigger..

Is this in first person? If so, the first person camera viewpoint is from a Bosmer's perspective, so Nords and High-Elves kind of see out of their neck/chest in first person.

No, this was in third person. However I did end up fixing it. All I did was crouch down, sat in a chair, and then my character grew back to his original height.

Was his/her legs like stuck in the floor, or was he/she just altogether smaller?

That's pretty weird.

No his legs were not stuck, just he was all together smaller.

Happens to me all the time Go into sneak and come back out.