I configured my github to only allow commits with an anonymised email address. Time passed and I used another machine on which I had already opened that repo before. I pulled my recent work successfully, wrote stuff and then committed and pushed.

Github rejected my commit as I had the wrong email address. I then had to try and work out how I delete a commit but keep all my changes so I could commit it all again but with the correct email address.

I'm not sure exactly what I did but in my ham-fisted experimentation I deleted the commit and restored my local copy back to the way it was before my commit, losing all my work that day.