Git Reflog - Restoring commits not shown in git log
Remarks
Git's reflog records the position of HEAD (the ref for the current state of the repository) every time that it is changed. Generally, every operation that might be destructive involves moving the HEAD pointer (since if anything is changed, including in the past, the tip commit's hash will change), so it is always possible to revert back to an older state, before a dangerous operation, by finding the right line in the reflog.
Objects that are not referenced by any ref are usually garbage collected in ~30 days, however, so the reflog may not always be able to help.
