Did you git reset --hard and lose work? Did a rebase eat a commit?
The commits are still there for ~30 days, just unreachable. Reflog finds them.
git reflog
# ...
# 4b5c6d7 HEAD@{2}: commit: feat: the lost work
# ...
Recover by resetting back:
git reset --hard 4b5c6d7
Or cherry-pick onto your current branch:
git cherry-pick 4b5c6d7
Or recreate a branch:
git branch rescued 4b5c6d7
Tip: the reflog is per-local-clone. If you cloned freshly and lost work pre-clone, the reflog won't help you — only a fresh git fetch from a remote that still has it.