ALT-H doesn’t do anything to that particular bone.
When I press H while in edit mode and have other bones selected, they hide and can be made visible with ALT-H again, except for the “hidden” bone I mentioned. Seems that they are two different kinds of “hidden”.
Bones have their own layering system. You may have put the bone on a different “bone layer” from the rest of the armature. To fix:
In the Armature panel, shift-select one-by-one the little boxes right under Display Options, to view the bone layers. If your bone appears, select it.
The Armature Bones panel has another row of little boxes. Click the first box to move your bone to that layer (which in your case is likely to contain all the rest of the bones).
Of course you could skip the second step and simply display all the layers that contain bones. Anyway does this help?
Thanks a lot. It seems I did indeed accidently switch layer instead of hiding it. Didn’t know the armature layers were different from the 3D view layers.