Trying to Make an Animation Work in Unity 5

I want to be able to hold right click to activate an animation (in this case, holding a gun up to the camera), play the last frame of the animation (so the gun stays there), then once right click stops being held, another animation (which is just the first one in reverse) plays. I've checked everywhere in the past like four days trying to find out how to do this, but I can't find anything that works (either doesn't work or is outdated).

The names of the animations:

The first one is 'GunAnimUp'

And the second is 'GunAnimDown'

Thanks! :D