This is what happened:
I have a branch A. On branch A I committed a bunch of changes. I was not happy with the code, so I checked out the previous commit in branch A. I then made a bunch more changes and committed them on branch A. Now I can not find this commit anywhere. Did I lose this code?
The old commit is still in the reflog.
This will show a list of commits, and the "lost" commit should be in there. You can make it into a new branch. For example, if the SHA-1 is ba5a739, then you can make a new branch named "new-branch" at the old commit with:
git branch new-branch ba5a739
Note that "lost" commits will get deleted when the database is pruned.