Not currently on any branch + git commit + checkout when not in any branch. Did I lose my changes?

You can use git reflog to get the commit hash of the commit that you did while in “no branch” ( a detached HEAD) and merge that in to the branch that you are currently in ( master maybe)

Something like git merge HEAD@{1}

You can also git rebase -i and “pick” the commit you want from the reflog.