Detached head means you are no longer on a branch, you have checked out a single commit in the history (in this case the commit previous to HEAD, i.e. HEAD^).

If you want to delete your changes associated with the detached HEAD

You only need to checkout the branch you were on, e.g.

git checkout master

Next time you have changed a file and want to restore it to the state it is in the index, don't delete the file first, just do

git checkout -- path/to/foo

This will restore the file foo to the state it is in the index.

If you want to keep your changes associated with the detached HEAD

  1. Run git branch tmp - this will save your changes in a new branch called tmp.
  2. Run git checkout master
  3. If you would like to incorporate the changes you made into master, run git merge tmp from the master branch. You should be on the master branch after running git checkout master.