Erasing you subsribed threads does just that, sorry, no way of getting them back that I know of. Then again I'm tech dense.

This link is the same as clicking on your username ("Upper left corner" in any post of yours). All the forums are not included in
this list for some reason, but most forums are and it is a fairly new feature as well. Maybe some of the forums will be included there later (like
"Fragile Earth").