Overencumbered through console commands.

[PurityChant]

So I put in a number that was too big using "player.modav carryweight" now my carryweight is a huge negative number. How can I fix this?

[fоreskin feta]

quick fix: use tgm (disables achievements)
real fix: set a lower, more realistic value

[Eternie]

Or go back to save from before you used that.

[E.P.D. Gaffney]

player.getavinfo carryweight
Whatever the override is is what you typed in, most likely, and you can just reverse it by reëntering the command using the same value but negative.

If the value is already negative on the override, you can use a positive value.

Do not use setav or forceav. Only modav.

[FaeVortex]

Literally just keep modav'ing positive values until the negative number wraps around back to a positive one.